Problem:
 Score : 500 points    Problem Statement You are given a string S of length N consisting of lowercase English letters.  Process Q queries of the following two types:   Type 1 : change the i_q -th character of S to c_q . (Do nothing if the i_q -th character is already c_q .)  Type 2 : answer the number of different characters occurring in the substring of S between the l_q -th and r_q -th characters (inclusive).       Constraints  N , Q , i_q , l_q , and r_q are integers.  S is a string consisting of lowercase English letters.  c_q is a lowercase English letter.  1 \leq N \leq 500000  1 \leq Q \leq 20000  |S| = N  1 \leq i_q \leq N  1 \leq l_q \leq r_q \leq N  There is at least one query of type 2 in each testcase.         Input Input is given from Standard Input in the following format:  N  S  Q  Query_1  \vdots  Query_Q   Here, Query_i in the 4 -th through (Q+3) -th lines is one of the following:  1  i_q  c_q   2  l_q  r_q       Output For each query of type 2 , print a line containing the answer.        Sample Input 1 7
abcdbbd
6
2 3 6
1 5 z
2 1 1
1 4 a
1 7 d
2 1 7      Sample Output 1 3
1
5  In the first query, cdbb contains three kinds of letters: b , c , and d , so we print 3 .  In the second query, S is modified to abcdzbd .  In the third query, a contains one kind of letter: a , so we print 1 .  In the fourth query, S is modified to abcazbd .  In the fifth query, S does not change and is still abcazbd .  In the sixth query, abcazbd contains five kinds of letters: a , b , c , d , and z , so we print 5 .

Solution (Python):
import bisect
import sys

input = sys.stdin.readline
num2alpha = lambda c: chr(c + 97)
alpha2num = lambda c: ord(c) - ord("a")


class SegTreeMax:
    def __init__(self, l):
        self.N = 1
        while self.N < l:
            self.N *= 2
        self.L = [0 for _ in range(self.N * 2 - 1)]

    def append(self, k, v):
        k += self.N - 1
        self.L[k] += 2 ** v
        while k > 0:
            k = (k - 1) // 2
            self.L[k] = self.L[k * 2 + 1] | self.L[k * 2 + 2]

    def delete(self, k, v):
        k += self.N - 1
        self.L[k] -= 2 ** v
        while k > 0:
            k = (k - 1) // 2
            self.L[k] = self.L[k * 2 + 1] | self.L[k * 2 + 2]

    def query(self, a, b):
        return self.inquiry(0, self.N, 0, a, b)

    def inquiry(self, l, r, k, a, b):
        if r <= a or l >= b:
            return 0
        if a <= l and b >= r:
            return self.L[k]
        vl = self.inquiry(l, (l + r) // 2, k * 2 + 1, a, b)
        vr = self.inquiry((l + r) // 2, r, k * 2 + 2, a, b)
        return vl | vr


def main():
    N = int(input())
    S = input()
    L = []
    for c in S:
        L.append(c)
    Q = int(input())
    T = SegTreeMax(N)
    for i in range(N):
        T.append(i, alpha2num(L[i]))

    for _ in range(Q):
        a, b, c = input().split()
        if a == "1":
            i = int(b) - 1
            T.delete(i, alpha2num(L[i]))
            L[i] = c
            T.append(i, alpha2num(c))

        else:
            l = int(b) - 1
            r = int(c)
            res = T.query(l, r)
            p = 0
            for i in range(26):
                p += res & 1
                res >>= 1
            print(p)


main()

Solution (Python):
import sys

def getN():
    return int(input())
def getNM():
    return map(int, input().split())
def getlist():
    return list(map(int, input().split()))
import math
import heapq
import bisect
from collections import defaultdict, Counter, deque
MOD = 10**9 + 7
INF = 10**21


class Segtree_op():
    def __init__(self, n):
        self.size = 1
        while (n >= 1):
            self.size = self.size << 1
            n = n // 2

        self.arr = [self.unit() for i in range(self.size * 2)]

    def op(self, lch, rch):
        
        return lch + rch

        
        
        
        
        

    def unit(self):
        return 0

    def update(self, k, val):
        k += self.size - 1
        self.arr[k] = val
        while (k):
            k = (k - 1) // 2
            self.arr[k] = self.op(self.arr[k * 2 + 1], self.arr[k * 2 + 2])

    def query(self, l, r):
        L = l + self.size
        R = r + self.size
        s = self.unit()
        while L < R:
            if R & 1:
                R -= 1
                s = self.op(s, self.arr[R - 1])

            if L & 1:
                s = self.op(s, self.arr[L - 1])
                L += 1
            L >>= 1
            R >>= 1
        return s

    
    
    
    
    


def main():
    n = getN()
    s = [c for c in input().strip()]
    q = getN()

    
    segs = [Segtree_op(n) for i in range(26)]
    for i, c in enumerate(s):
        segs[ord(c) - ord("a")].update(i, 1)

    for query in range(q):
        operand, a, b = input().split()
        if operand == "1":
            
            a = int(a) - 1
            segs[ord(s[a]) - ord("a")].update(a, 0)
            segs[ord(b) - ord("a")].update(a, 1)
            s[a] = b

        else:  
            tmp = 0
            
            a, b = int(a) - 1, int(b) - 1
            for se in segs:
                
                
                if se.query(a, b+1) > 0:
                    tmp += 1
            print(tmp)

    

if __name__ == '__main__':
    main()

"""
7 
aaaabbb
3
1 7 c
2 1 5
2 1 7
>> 2
>> 3


26 
abcdefghijklmnopqrstuvwxyz
7
2 1 26
2 2 26
2 5 5
2 11 20
2 25 26 
1 1 z
2 1 26
>> 26
>> 25
>> 1
>> 10
>> 2
>> 25
"""

Solution (Python):
import sys
input=sys.stdin.readline
from string import ascii_lowercase

class BIT(): 
    def __init__(self,n): 
        self.size=n
        self.bit=[0]*(n+1)
    def add(self,i,x): 
        while i<=self.size:
            self.bit[i]+=x
            i+=i&-i
    def sum_1_to_i(self,i): 
        s=0
        while i>0:
            s+=self.bit[i]
            i-=i&-i
        return s
    def sum_i_to_j(self,i,j): 
        return self.sum_1_to_i(j)-self.sum_1_to_i(i-1)
    def reset(self): 
        self.bit=[0]*(self.size+1)

def main():
    A=ascii_lowercase
    D=dict()
    for i,a in enumerate(A):
        D[a]=i
    n=int(input())
    S=list(input().strip())
    L=[BIT(n) for _ in range(26)]
    for i,s in enumerate(S):
        L[D[s]].add(i+1,1)
    q=int(input())
    for _ in range(q):
        k,a,b=input().split()
        if k=='1':
            i=int(a)-1
            s=S[i]
            L[D[b]].add(i+1,1)
            L[D[s]].add(i+1,-1)
            S[i]=b
        else:
            l=int(a); r=int(b)
            ans=0
            for i in range(26):
                ans+=L[i].sum_i_to_j(l,r)>0
            print(ans)
    
if __name__=='__main__':
    main()

Solution (Python):
import bisect
import sys

input = sys.stdin.readline
num2alpha = lambda c: chr(c + 97)
alpha2num = lambda c: ord(c) - ord("a")


class SegTreeMax:
    def __init__(self, l):
        self.N = 1
        while self.N < l:
            self.N *= 2
        self.L = [0 for _ in range(self.N * 2 - 1)]

    def update(self, k, v):
        k += self.N - 1
        self.L[k] = v
        while k > 0:
            k = (k - 1) // 2
            self.L[k] = max(self.L[k * 2 + 1], self.L[k * 2 + 2])

    def append(self, k, v):
        k += self.N - 1
        self.L[k] += 2 ** v
        while k > 0:
            k = (k - 1) // 2
            self.L[k] = self.L[k * 2 + 1] | self.L[k * 2 + 2]

    def delete(self, k, v):
        k += self.N - 1
        self.L[k] -= 2 ** v
        while k > 0:
            k = (k - 1) // 2
            self.L[k] = self.L[k * 2 + 1] | self.L[k * 2 + 2]

    def query(self, a, b):
        return self.inquiry(0, self.N, 0, a, b)

    def inquiry(self, l, r, k, a, b):
        if r <= a or l >= b:
            return 0
        if a <= l and b >= r:
            return self.L[k]
        vl = self.inquiry(l, (l + r) // 2, k * 2 + 1, a, b)
        vr = self.inquiry((l + r) // 2, r, k * 2 + 2, a, b)
        return vl | vr


def main():
    N = int(input())
    Stri = input()
    L = []
    for c in Stri:
        L.append(c)
    Q = int(input())
    S = SegTreeMax(N)
    for i in range(N):
        S.append(i, alpha2num(L[i]))

    for _ in range(Q):
        a, b, c = input().split()
        if a == "1":
            i = int(b) - 1
            S.delete(i, alpha2num(L[i]))
            L[i] = c
            S.append(i, alpha2num(c))

        else:
            l = int(b) - 1
            r = int(c)
            res = S.query(l, r)
            p = 0
            for i in range(26):
                p += res & 1
                res >>= 1
            print(p)


main()

Solution (Python):
from collections import Counter
def snum(x):
    return ord(x)-ord('a')

class Bit:
    def __init__(self, n,ls):
        self.size=n
        self.tree=[[0]*26 for _ in range(n+1)]
        self.ls=['']*(n+1)

    def sum(self, i, j):
        i-=1
        res=[0]*26
        for k in range(26):
            i2=i
            j2=j
            while j2>0:
                res[k] += self.tree[j2][k]
                j2 -= j2&-j2
            while i2>0:
                res[k] -= self.tree[i2][k]
                i2 -= i2&-i2
        return 26-res.count(0)
    
    def add(self, i, x):
        self.ls[i] = x
        while i <= self.size:
            self.tree[i][snum(x)]+=1
            i += i & -i

    def change(self, i, x):
        original = self.ls[i]
        self.ls[i]=x
        while i <= self.size:
            self.tree[i][snum(original)] -= 1
            self.tree[i][snum(x)] += 1
            i += i & -i
        

n = int(input())
s = list(input())
bit=Bit(n,s)

for i in range(n):
    bit.add(i+1, s[i])

q = int(input())
for _ in range(q):
    query, a, b = input().split()
    if query=='1':
        bit.change(int(a),b)
    else:
        print(bit.sum(int(a), int(b)))

Solution (Python):
class SegmentTree:
    def __init__(self, a):    
        self.n = len(a)
        self.N = 2 ** (self.n-1).bit_length()
        l = []
        for _a in a:
            l.append(1 << ord(_a)-97)
        self.data = [0]*(self.N-1) + l + [0]*(self.N-self.n)
        for i in range(2*self.N-2, 0, -2):
            self.data[(i-1)//2] = self.data[i] | self.data[i-1]
    
    def update(self, i, x):
        idx = self.N - 1 + i
        self.data[idx] = 1 << ord(x)-97
        while idx:
            idx = (idx-1) // 2
            self.data[idx] = self.data[2*idx+1] | self.data[2*idx+2]
    
    def query(self, i, j):
        
        if i == j:
            return bin(self.data[self.N - 1 + i]).count('1')
        else:
            idx1 = self.N - 1 + i
            idx2 = self.N - 2 + j 
            b = 0
            while idx1 + 1 < idx2:
                if idx1&1 == 0: 
                    b = b | self.data[idx1]
                if idx2&1 == 1: 
                    b = b | self.data[idx2]
                    idx2 -= 1
                
                idx1 //= 2
                idx2 = (idx2 - 1)//2
            
            if idx1 == idx2:
                b = b | self.data[idx1]
            else: 
                b = b | self.data[idx1] | self.data[idx2]
            
            return bin(b).count('1')

N = int(input())
S = list(input())
st = SegmentTree(S)

Q = int(input())
for i in range(Q):
  t, a, b = input().split()
  if t == '1':
    a = int(a)
    if S[a-1] == b:
      continue
    st.update(a-1, b)
    S[a-1] = b
  else:
    a, b = int(a), int(b)
    print(st.query(a-1, b))

Solution (Python):

import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict, deque
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product, permutations
from operator import add, mul, sub, or_

sys.setrecursionlimit(100000)
input = sys.stdin.readline
INF = 2**62-1

def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input().strip()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args):
    print(*args, file=sys.stderr)



def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()

        error_print(e - s, 'sec')
        return ret

    return wrap


class SegmentTree():
    
    
    def __init__(self, N, operator, identity_element):
        """ operator and identity_element has to be a monoid.
        """
        self.__N = 2**int(math.ceil(math.log(N, 2)))
        self.__table = [identity_element] * (self.__N * 2 - 1)
        self.__op = operator
        self.__ie = identity_element

    def update(self, idx, x):
        i = self.__N - 1 + idx  
        t = self.__table
        o = self.__op

        t[i] = x
        while i != 0:
            pi = (i - 1) // 2  
            li = 2*pi + 1
            ri = 2*pi + 2
            v = o(t[li], t[ri])
            if t[pi] != v:
                t[pi] = v
            else:
                break
            i = pi

    def query(self, a, b):
        stack = [(0, 0, self.__N)]
        t = self.__table
        o = self.__op

        ans = self.__ie
        c = 0
        while stack:
            c += 1
            k, l, r = stack.pop()
            cnd = t[k]
            if a <= l and r <= b:
                ans = o(ans, cnd)
            else:
                if (l + r) // 2 > a and b > l:
                    stack.append((2 * k + 1, l, (l + r) // 2))

                if r > a and b > (l + r) // 2:
                    stack.append((2 * k + 2, (l + r) // 2, r))
        return ans

    def print(self):
        print(self.__table)



@mt
def slv(N, S, Q):
    S = [c for c in S]
    st = SegmentTree(N, or_, 0)
    for i, c in enumerate(S):
        st.update(i, 1 << (ord(c) - ord('a')))

    for q in Q:
        if q[0] == '1':
            i = int(q[1]) - 1
            c = q[2]
            st.update(i, 1 << (ord(c) - ord('a')))
        if q[0] == '2':
            i = int(q[1]) - 1
            j = int(q[2]) - 1
            ans = 0
            v = st.query(i, j+1)
            for k in range(26):
                if (1 << k) & v:
                    ans += 1
            print(ans)
    


def main():
    N = read_int()
    S = read_str()
    Q = [read_str_n() for _ in range(read_int())]
    (slv(N, S, Q))

if __name__ == '__main__':
    main()

Solution (Python):
import sys
input = sys.stdin.readline
N = int(input())
S = input()
Q = int(input())

ide_ele = 0

def segfunc(x,y):
    return x|y

def init(init_val):
    
    for i in range(N):
        seg[i+num-1]=1<<(ord(init_val[i])-ord('a'))
    
    for i in range(num-2,-1,-1) :
        seg[i]=segfunc(seg[2*i+1],seg[2*i+2]) 
    
def update(k,x):
    k += num-1
    x = 1<<(ord(x)-ord('a'))
    if x == seg[k]: return
    seg[k] = x
    while k:
        k = (k-1)//2
        seg[k] = segfunc(seg[k*2+1],seg[k*2+2])
    
def query(p,q):
    if q<=p:
        return ide_ele
    p += num-1
    q += num-2
    res=ide_ele
    while q-p>1:
        if p&1 == 0:
            res = segfunc(res,seg[p])
        if q&1 == 1:
            res = segfunc(res,seg[q])
            q -= 1
        p = p//2
        q = (q-1)//2
    if p == q:
        res = segfunc(res,seg[p])
    else:
        res = segfunc(segfunc(res,seg[p]),seg[q])
    return res


num =2**(N-1).bit_length()
seg=[ide_ele]*2*num

init(S)

for _ in range(Q):
    t, a, b = input().split()
    if t == '1':
        a = int(a)
        update(a-1, b)
    else:
        a, b = int(a)-1, int(b)
        print(bin(query(a,b)).count('1'))

Solution (Python):

from collections import defaultdict,deque
from heapq import heappush, heappop
from bisect import bisect_left, bisect_right
import sys, random, itertools, math
sys.setrecursionlimit(10**5)
input = sys.stdin.readline
sqrt = math.sqrt
def LI(): return list(map(int, input().split()))
def LF(): return list(map(float, input().split()))
def LI_(): return list(map(lambda x: int(x)-1, input().split()))
def II(): return int(input())
def IF(): return float(input())
def LS(): return input().split()
def S(): return list(input().rstrip())
def IR(n): return [II() for _ in range(n)]
def LIR(n): return [LI() for _ in range(n)]
def FR(n): return [IF() for _ in range(n)]
def LFR(n): return [LI() for _ in range(n)]
def LIR_(n): return [LI_() for _ in range(n)]
def SR(n): return [S() for _ in range(n)]
def LSR(n): return [LS() for _ in range(n)]
mod = 1000000007
inf = float('INF')


class BinaryIndexedTree:
    
    def __init__(self, size):
        """
        :param int size:
        """
        self.bit = [0 for _ in range(size)]
        self.size = size

    def add(self, i, w):
        """
        i番目にwを加える
        :param int i:
        :param int w:
        :return:
        """
        x = i + 1
        while x <= self.size:
            self.bit[x - 1] += w
            x += x & -x
        return

    def sum(self, i):
        """
        [0,i]の合計
        :param int i:
        :return:
        """
        res = 0
        x = i + 1
        while x > 0:
            res += self.bit[x - 1]
            x -= x & -x
        return res

    def search(self, x):
        """
        二分探索。和がx以上となる最小のインデックス(>= 1)を返す
        :param int x:
        :return :
        """
        i = 1
        s = 0
        step = 1 << (self.size.bit_length() - 1)
        while step:
            if i + step <= self.size and s + self.bit[i + step - 1] < x:
                i += step
                s += self.bit[i - 1]
            step >>= 1
        return i

    def __len__(self):
        return self.size


def solve():
    n = II()
    s = S()
    q = II()
    ans = [BinaryIndexedTree(n + 1) for i in range(27)]
    lis = [ord(si) - ord("a") for si in s]
    for i in range(n):
        ans[lis[i]].add(i+1, 1)
    for _ in range(q):
        t, i, c = LS()
        i = int(i)
        if t == "1":
            ans[lis[i-1]].add(i, -1)
            ans[ord(c) - ord("a")].add(i, 1)
            lis[i-1] = ord(c) - ord("a")
        else:
            l = i - 1
            r = int(c)
            res = 0
            for i in range(27):
                res += ans[i].sum(r) - ans[i].sum(l) > 0
            print(res)
    


    return



if __name__ == '__main__':
    solve()

Solution (Python):
import sys
from collections import defaultdict


class SegTree:
    """
    今回の問題に特化したセグ木
    """

    def __init__(self, n, s):
        """
        :param n: 文字列長
        :param s: 初期文字列
        """
        n2 = 1 << (n - 1).bit_length()
        self.offset = n2
        self.tree = [None] * n2 + [{} for _ in range(n2)]
        lmd0 = lambda: 0

        for i, c in enumerate(s):
            x = ord(c) - 97
            i += self.offset
            self.tree[i][x] = 1
        for i in range(self.offset - 1, 0, -1):
            sti = self.tree[i] = defaultdict(lmd0, self.tree[i << 1])
            stj = self.tree[(i << 1) + 1]
            for x in stj:
                sti[x] += stj[x]
        

    def update(self, i, x):
        """
        i番目の値をxに変更
        :param i: index(0-indexed)
        :param x: update value
        """
        i += self.offset
        if x in self.tree[i]:
            return
        y, _ = self.tree[i].popitem()
        self.tree[i][x] = 1
        i >>= 1
        while i > 0:
            sti = self.tree[i]
            sti[x] += 1
            if sti[y] == 1:
                del sti[y]
            else:
                sti[y] -= 1
            i >>= 1

    def get_types(self, a, b):
        """
        [a, b)の文字種数を得る
        :param a: index(0-indexed)
        :param b: index(0-indexed)
        """
        result = set()

        l = a + self.offset
        r = b + self.offset
        while l < r:
            if r & 1:
                result.update(self.tree[r - 1].keys())
            if l & 1:
                result.update(self.tree[l].keys())
                l += 1
            l >>= 1
            r >>= 1

        return len(result)


n = int(input())
s = input()
st = SegTree(n, s)
q = int(input())
ans = []
for line in sys.stdin:
    i, j, k = line.rstrip().split()
    if i == '1':
        j = int(j) - 1
        k = ord(k) - 97
        st.update(j, k)
    else:
        l = int(j) - 1
        r = int(k)
        ans.append(st.get_types(l, r))
print('\n'.join(map(str, ans)))

Solution (Python):
import sys
import bisect
n = int(sys.stdin.readline().strip())
s = list(sys.stdin.readline().strip())
alpha = "abcdefghijklmnopqrstuvwxyz"
dict = {i:[] for i in alpha}
for i, _s in enumerate(s):
    dict[_s].append(i)
q = int(sys.stdin.readline().strip())
for i in range(q):
    type, first, last = [i for i in sys.stdin.readline().split()]
    if type == "2":
        first = int(first)
        last = int(last)
        first -= 1
        last -= 1
        cnt = 0
        for ls in dict.values():
            if bisect.bisect_left(ls, first) != bisect.bisect_right(ls, last):
                cnt += 1
        print(cnt)
    else:
        first = int(first)
        first -= 1
        _s = s[first]
        if _s == last:
            continue
        del dict[_s][(bisect.bisect_left(dict[_s], first))]
        s[first] = last
        bisect.insort_left(dict[last], first)

Solution (Python):
import sys
from collections import defaultdict


class SegTree:
    def __init__(self, n, s):
        """
        :param n: 要素数
        :param INF: 初期値（入りうる要素より十分に大きな数）
        """
        n2 = 1 << (n - 1).bit_length()
        self.offset = n2
        self.tree = [None] * n2 + [{} for _ in range(n2)]
        self.lmd0 = lambda: 0

        for i, c in enumerate(s):
            x = ord(c) - 97
            i += self.offset
            self.tree[i][x] = 1
        for i in range(self.offset - 1, 0, -1):
            sti = self.tree[i] = defaultdict(self.lmd0, self.tree[i << 1])
            stj = self.tree[(i << 1) + 1]
            for x in stj:
                sti[x] += stj[x]
        

    def update(self, i, x):
        """
        i番目の値をxに更新
        :param i: index(0-indexed)
        :param x: update value
        """
        i += self.offset
        if x in self.tree[i]:
            return
        y, _ = self.tree[i].popitem()
        self.tree[i][x] = 1
        i >>= 1
        while i > 0:
            sti = self.tree[i]
            sti[x] += 1
            if sti[y] == 1:
                del sti[y]
            else:
                sti[y] -= 1
            i >>= 1

    def get_types(self, a, b):
        """
        [a, b)の最小値を得る
        :param a: index(0-indexed)
        :param b: index(0-indexed)
        """
        result = set()

        l = a + self.offset
        r = b + self.offset
        while l < r:
            if r & 1:
                result.update(self.tree[r - 1].keys())
            if l & 1:
                result.update(self.tree[l].keys())
                l += 1
            l >>= 1
            r >>= 1

        return len(result)


n = int(input())
s = input()
st = SegTree(n, s)
q = int(input())
ans = []
for line in sys.stdin:
    i, j, k = line.rstrip().split()
    if i == '1':
        j = int(j) - 1
        k = ord(k) - 97
        st.update(j, k)
    else:
        l = int(j) - 1
        r = int(k)
        ans.append(st.get_types(l, r))
print('\n'.join(map(str, ans)))

Solution (Python):
class SegmentTree:
	def __init__(self, orig, func, unit):
		_len = len(orig)
		self.func = func
		self.size = 1 << (_len - 1).bit_length()
		self.tree = [unit] * self.size + orig + [unit] * (self.size - _len)
		self.unit = unit

		for i in range(self.size - 1, 0, -1):
			self.tree[i] = func(self.tree[i * 2], self.tree[i * 2 + 1])

	def update(self, i, v):
		i += self.size
		self.tree[i] = v
		while i:
			i //= 2
			self.tree[i] = self.func(self.tree[i * 2], self.tree[i * 2 + 1])

	def find(self, l, r):
		l += self.size
		r += self.size
		ret = self.unit
		while l < r:
			if l & 1:
				ret = self.func(ret, self.tree[l])
				l += 1
			if r & 1:
				r -= 1
				ret = self.func(ret, self.tree[r])
			l //= 2
			r //= 2
		return ret

import sys
input = sys.stdin.readline
from operator import or_

def main():
	input()
	seg = SegmentTree([1 << ord(x) - 97 for x in input()[:-1]], or_, 0)
	ans = []
	for _ in range(int(input())):
		f, x, y = input().split()
		if f == "1":
			seg.update(int(x) - 1, 1 << ord(y) - 97)
		else:
			ans.append(bin(seg.find(int(x) - 1, int(y))).count("1"))
	print(*ans)

if __name__=="__main__":
	main()

Solution (Python):
class SegmentTree():
    def __init__(self,arr,func=min,ie=2**63):
        self.n = 2**(len(arr)-1).bit_length()
        self.ie = ie
        self.func = func
        self.tree = [ie for _ in range(2*self.n)]
        for i in range(len(arr)):
            self.tree[self.n+i-1] = arr[i]
        for i in range(self.n-1)[::-1]:
            self.tree[i] = func(self.tree[2*i+1],self.tree[2*i+2])

    def set(self,index,x):
        index += self.n-1
        self.tree[index] = x
        while index:
            index = (index-1)//2
            self.tree[index] = self.func(self.tree[2*index+1],self.tree[2*index+2])

    def query(self,left,right):
        if right <= left:
            return self.ie
        left += self.n-1
        right += self.n-2
        tmp_l = self.ie
        tmp_r = self.ie
        while right-left>1:
            if left & 1 == 0:
                tmp_l = self.func(tmp_l,self.tree[left])
            if right & 1 == 1:
                tmp_r = self.func(self.tree[right],tmp_r)
                right -= 1
            left = left//2
            right = (right-1)//2
        if left == right:
            tmp_l = self.func(tmp_l,self.tree[left])
        else:
            tmp_l = self.func(self.func(tmp_l,self.tree[left]),self.tree[right])
        return self.func(tmp_l,tmp_r)

import sys
input = sys.stdin.readline

N = int(input())
S = input()
Q = int(input())

A = []
for i in range(N):
    A.append(set([ord(S[i])-97]))

def func(x,y):
    return x|y
ie = set()

st = SegmentTree(A,func,ie)

ans = []

for _ in range(Q):
    q,x,y = input().split()
    q = int(q)
    if q == 1:
        st.set(int(x)-1,set([ord(y)-97]))
    else:
        ans.append(len(st.query(int(x)-1,int(y))))

print('\n'.join(map(str,ans)))

Solution (Python):
import sys
read = sys.stdin.readline


def read_ints():
    return list(map(int, read().split()))


def read_a_int():
    return int(read())


def read_matrix(H):
    '''
    H is number of rows
    '''
    return [list(map(int, read().split())) for _ in range(H)]


def read_map(H):
    '''
    H is number of rows
    文字列で与えられた盤面を読み取る用
    '''
    return [read()[:-1] for _ in range(H)]


def read_tuple(H):
    '''
    H is number of rows
    '''
    ret = []
    for _ in range(H):
        ret.append(tuple(map(int, read().split())))
    return ret


def read_col(H, n_cols):
    '''
    H is number of rows
    n_cols is number of cols

    A列、B列が与えられるようなとき
    '''
    ret = [[] for _ in range(n_cols)]
    for _ in range(H):
        tmp = list(map(int, read().split()))
        for col in range(n_cols):
            ret[col].append(tmp[col])

    return ret


def index(a, x):
    'Locate the leftmost value exactly equal to x'
    i = bisect_left(a, x)

    if i != len(a) and a[i] == x:
        return i
    raise ValueError









N = read_a_int()
S = list(read()[:-1])

from collections import defaultdict
from bisect import bisect_left, bisect_right, insort_left
char_idxs = defaultdict(lambda: [])
for i, s in enumerate(S):
    char_idxs[s].append(i)


def get_syurui(char_idxs, l, r):
    ret = 0
    for v in char_idxs.values():
        l_idx = bisect_left(v, l)
        r_idx = bisect_right(v, r)
        
        if r_idx - l_idx > 0:
            ret += 1
    return ret


Q = read_a_int()
for q in range(Q):
    com, a, b = read().split()
    if int(com) == 2:
        a, b = int(a) - 1, int(b) - 1
        print(get_syurui(char_idxs, a, b))
    else:
        i = int(a) - 1
        if S[i] == b:
            continue
        
        tmp = char_idxs[S[i]]  
        del char_idxs[S[i]][index(tmp, i)]
        
        insort_left(char_idxs[b], i)
        
        S[i] = b

Solution (Python):
"""
E
"""

def bit_add(I,k):
    while I<=N:
        tree[k][I]+=1
        I+=I&(-I)

def bit_no_add(I,k):
    while I<=N:
        tree[k][I]-=1
        I+=I&(-I)
        

def bit_sum(I,k):
    s=0
    while I>0:
        s+=tree[k][I]
        I-=I&(-I)
    return s

N=int(input())
S=["a"]+list(input())
Q=int(input())
que=[list(input().split()) for i in range(Q)]

alpa=list("abcdefghijklmnopqrstuvwxyz")
tree=[[0]*(N+1) for i in range(len(alpa))]

for i in range(1,N+1):
    j=alpa.index(S[i])
    bit_add(i, j)

for iii in range(Q):
    if que[iii][0]=="1":
        i,c=int(que[iii][1]),que[iii][2]
        j=alpa.index(S[i])
        bit_no_add(i, j)
        S[i]=c
        j=alpa.index(c)
        bit_add(i, j)
    else:
        l,r=que[iii][1],que[iii][2]
        l=int(l)
        r=int(r)
        cnt=0
        for j in range(len(alpa)):
            if bit_sum(l-1, j)==bit_sum(r, j):
                continue
            cnt+=1
        print(cnt)

Solution (Python):
from collections import defaultdict

alpha = defaultdict(int)
num = 0
for i in sorted(map(chr,range(97,123))):
    alpha[i] = 1 << num
    num += 1

n = int(input())
S = tuple(alpha[i] for i in input())

def init(init_val):
    
    for i in range(n):
        seg[i+num-1] = init_val[i]
    
    for i in range(num-2,-1,-1):
        seg[i] = seg[2*i+1] | seg[2*i+2]
    
def update(k,x):
    k += num-1
    seg[k] = x
    while k:
        k = (k-1)//2
        seg[k] = seg[k*2+1] | seg[k*2+2]
    
def query(p,q):
    if q<=p:
        return 0
    p += num-1
    q += num-2
    res=0
    while q-p>1:
        if p&1 == 0:
            res |= seg[p]
        if q&1 == 1:
            res |= seg[q]
            q -= 1
        p = p//2
        q = (q-1)//2
    if p == q:
        res |= seg[p]
    else:
        res |= (seg[p] | seg[q])
    cnt = 0
    i = 0
    while res:
        cnt += res & 1
        i += 1
        res >>= 1
    return cnt

num =2**(n-1).bit_length()
seg=[0 for _ in range(2*num)]

init(S)

Q = int(input())
for _ in range(Q):
    x,y,z = map(str,input().split())
    x = int(x); y = int(y)
    if x == 1:
        update(y-1, alpha[z])
    else:
        z = int(z)
        print(query(y-1,z))

Solution (Python):
import math
import collections

N = int(input())
S = input()

S = list(S)
def bit_add(A,a,w): 
    ind = a

    while len(A) > ind:
        A[ind] += w
        lsb = ind & (-ind)
        
        ind += lsb

    return

def bit_sum(A, a):  
    s = 0
    ind = a
    while ind != 0:
        s += A[ind]
        lsb = ind & (-ind)
        ind -= lsb

    return s

li = {}
for c in "abcdefghijklmnopqrstuvwxyz":
    li[c] = [0] * (N + 1)

for i in range(1,N + 1):
    char = S[i - 1]
    bit_add(li[char],i,1)



Q = int(input())
queries = [input().split() for _ in range(Q)]
for query in queries:
    a,b,c = query
    a = int(a)
    b = int(b)
    if a == 1: 
        i = b

        c_org = S[i - 1] 
        
        S[i - 1] = c
        bit_add(li[c_org], i,  -1)
        bit_add(li[c], i, 1) 

    if a == 2:
        ans = 0
        l = b
        r = int(c)
        for c in "abcdefghijklmnopqrstuvwxyz":
            temp = li[c]
            r_sum = bit_sum(temp,r)
            l_sum = bit_sum(temp,l - 1)
            diff = r_sum-l_sum
            if diff > 0: 
                ans += 1
        print(ans)