Buggy python submission (verdict: Runtime Error):
import sys
input = lambda: sys.stdin.readline().rstrip()
from operator import or_

def popcount(x):
    x -= (x >> 1) & 0x55555555
    x = (x & 0x33333333) + ((x >> 2) & 0x33333333)
    x = (x + (x >> 4)) & 0x0f0f0f0f
    x += x >> 8
    x += x >> 16
    return x & 0x3f

class SegmentTree():
    def __init__(self, n, unit, f, initial = []):
        self.f = f
        self.unit = unit
        k = (n-1).bit_length()
        nn = 1 << k + 1
        self.leaf = 1 << k
        if not len(initial):
            self.X = [unit] * nn
        else:
            self.X = [unit] * self.leaf + initial + [unit] * (self.leaf - len(initial))
            for i in range(self.leaf)[::-1]:
                self.X[i] = self.f(self.X[2*i], self.X[2*i+1])
    
    def update(self, i, x):
        i += self.leaf
        self.X[i] = x
        i //= 2
        while i:
            self.X[i] = self.f(self.X[2*i], self.X[2*i+1])
            i //= 2
    
    def query(self, l, r):
        l += self.leaf
        r += self.leaf
        s = self.unit
        while l < r:
            if l & 1:
                s = self.f(self.X[l], s)
                l += 1
            if r & 1:
                r -= 1
                s = self.f(s, self.X[r])
            l >>= 1
            r >>= 1
        return s
    
    def debug(self):
        i = 1
        while i <= self.leaf:
            print(self.X[i:i*2])
            i *= 2
    def debug(self):
        i = 1
        while i <= self.leaf:
            print([bin(a) for a in self.X[i:i*2]])
            i *= 2

N = int(input())
S = [1 << ord(a) - 97 for a in input()]
st = SegmentTree(26, 0, or_, S)

M = int(input())
for _ in range(M):
    a, b, c = input().split()
    if a == "1":
        b = int(b)
        st.update(b-1, 1 << ord(c) - 97)
    else:
        b, c = int(b)-1, int(c)-1
        print(popcount(st.query(b, c + 1)))

Fixed submission:
N = int(input())
A = [ord(a) - 97 for a in input()]
NN = 19
BIT=[[0]*(2**NN+1) for _ in range(26)]
 
def addbit(t, i, x):
    while i <= 2**NN:
        BIT[t][i] += x
        i += i & (-i)

def getsum(t, i):
    ret = 0
    while i != 0:
        ret += BIT[t][i]
        i -= i&(-i)
    return ret

for i, a in enumerate(A):
    BIT[a][i+1] += 1

for t in range(26):
    B = [0] * (2**NN+1)
    for i in range(1<<NN):
        B[i+1] = B[i] + BIT[t][i]
    for i in range(1<<NN):
        BIT[t][i] = B[i] - B[i - (i & (-i))]

Q = int(input())
for _ in range(Q):
    a, b, c = input().rstrip().split()
    if a == "1":
        b = int(b)
        c = ord(c) - 97
        t = A[b-1]
        addbit(t, b+1, -1)
        addbit(c, b+1, 1)
        A[b-1] = c
    else:
        b, c = int(b), int(c)
        s = 0
        for t in range(26):
            s += 1 if getsum(t, c+1) - getsum(t, b) else 0
        print(s)

Buggy python submission (verdict: Runtime Error):
NN = 19
NN = 5
X = [0] * ((1<<NN+1)-1)
 
def popcount(x):
    x -= (x >> 1) & 0x55555555
    x = (x & 0x33333333) + ((x >> 2) & 0x33333333)
    x = (x + (x >> 4)) & 0x0f0f0f0f
    x += x >> 8
    x += x >> 16
    return x & 0x3f

def update(a, x):
    i = (1<<NN) - 1 + a
    X[i] = x
    while True:
        i = (i-1) // 2
        X[i] = X[2*i+1] | X[2*i+2]
        if i == 0:
            break

def rangeor(a, b):
    l = a + (1<<NN)
    r = b + (1<<NN)
    x = 0
    while l < r:
        if l%2:
            x |= X[l-1]
            l += 1
        if r%2:
            r -= 1
            x |= X[r-1]
        l >>= 1
        r >>= 1
    return x

N = int(input())
A = [ord(a) - 97 for a in input()]
for i, a in enumerate(A):
    X[(1<<NN) + i] = 1 << a
for i in range((1<<NN)-1)[::-1]:
    X[i] = X[i*2+1] | X[i*2+2]

Q = int(input())
for _ in range(Q):
    a, b, c = input().rstrip().split()
    if a == "1":
        b = int(b)
        c = ord(c) - 97
        update(b, 1<<c)
    else:
        b, c = int(b), int(c)
        print(popcount(rangeor(b, c+1)))
        print([i for i in range(26) if rangeor(b, c+1)>>i & 1])

Fixed submission:
N = int(input())
A = [ord(a) - 97 for a in input()]
NN = 19
BIT=[[0]*(2**NN+1) for _ in range(26)]
 
def addbit(t, i, x):
    while i <= 2**NN:
        BIT[t][i] += x
        i += i & (-i)

def getsum(t, i):
    ret = 0
    while i != 0:
        ret += BIT[t][i]
        i -= i&(-i)
    return ret

for i, a in enumerate(A):
    BIT[a][i+1] += 1

for t in range(26):
    B = [0] * (2**NN+1)
    for i in range(1<<NN):
        B[i+1] = B[i] + BIT[t][i]
    for i in range(1<<NN):
        BIT[t][i] = B[i] - B[i - (i & (-i))]

Q = int(input())
for _ in range(Q):
    a, b, c = input().rstrip().split()
    if a == "1":
        b = int(b)
        c = ord(c) - 97
        t = A[b-1]
        addbit(t, b+1, -1)
        addbit(c, b+1, 1)
        A[b-1] = c
    else:
        b, c = int(b), int(c)
        s = 0
        for t in range(26):
            s += 1 if getsum(t, c+1) - getsum(t, b) else 0
        print(s)

Buggy python submission (verdict: Runtime Error):
N = int(input())
A = [ord(a) - 97 for a in input()]
NN = 5
BIT=[[0]*(2**NN+1) for _ in range(26)]
 
def addbit(t, i, x):
    while i <= 2**NN:
        BIT[t][i] += x
        i += i & (-i)

def getsum(t, i):
    ret = 0
    while i != 0:
        ret += BIT[t][i]
        i -= i&(-i)
    return ret


for i, a in enumerate(A):
    BIT[a][i+1] += 1

for t in range(26):
    B = [0] * (2**NN+1)
    for i in range(1<<NN):
        B[i+1] = B[i] + BIT[t][i]
    for i in range(1<<NN):
        BIT[t][i] = B[i] - B[i - (i & (-i))]

Q = int(input())
for _ in range(Q):
    a, b, c = input().split()
    if a == "1":
        b = int(b)
        c = ord(c) - 97
        t = A[b-1]
        addbit(t, b, -1)
        addbit(c, b, 1)
    else:
        b, c = int(b), int(c)
        s = 0
        for t in range(26):
            s += 1 if getsum(t, c+1) - getsum(t, b) else 0
        print(s)

Fixed submission:
N = int(input())
A = [ord(a) - 97 for a in input()]
NN = 19
BIT=[[0]*(2**NN+1) for _ in range(26)]
 
def addbit(t, i, x):
    while i <= 2**NN:
        BIT[t][i] += x
        i += i & (-i)

def getsum(t, i):
    ret = 0
    while i != 0:
        ret += BIT[t][i]
        i -= i&(-i)
    return ret

for i, a in enumerate(A):
    BIT[a][i+1] += 1

for t in range(26):
    B = [0] * (2**NN+1)
    for i in range(1<<NN):
        B[i+1] = B[i] + BIT[t][i]
    for i in range(1<<NN):
        BIT[t][i] = B[i] - B[i - (i & (-i))]

Q = int(input())
for _ in range(Q):
    a, b, c = input().rstrip().split()
    if a == "1":
        b = int(b)
        c = ord(c) - 97
        t = A[b-1]
        addbit(t, b+1, -1)
        addbit(c, b+1, 1)
        A[b-1] = c
    else:
        b, c = int(b), int(c)
        s = 0
        for t in range(26):
            s += 1 if getsum(t, c+1) - getsum(t, b) else 0
        print(s)

Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline
N = int(input())
A = [ord(a) - 97 for a in input()]
NN = 19
BIT=[[0]*(2**NN+1) for _ in range(26)]
 
def addbit(t, i, x):
    while i <= 2**NN:
        BIT[t][i] += x
        i += i & (-i)

def getsum(t, i):
    ret = 0
    while i != 0:
        ret += BIT[t][i]
        i -= i&(-i)
    return ret


for i, a in enumerate(A):
    BIT[a][i+1] += 1

for t in range(26):
    B = [0] * (2**NN+1)
    for i in range(1<<NN):
        B[i+1] = B[i] + BIT[t][i]
    for i in range(1<<NN):
        BIT[t][i] = B[i] - B[i - (i & (-i))]

Q = int(input())
for _ in range(Q):
    a, b, c = input().split()
    if a == "1":
        b = int(b)
        c = ord(c) - 97
        t = A[b-1]
        addbit(t, b, -1)
        addbit(c, b, 1)
    else:
        b, c = int(b), int(c)
        s = 0
        for t in range(26):
            s += 1 if getsum(t, c+1) - getsum(t, b) else 0
        print(s)

Fixed submission:
N = int(input())
A = [ord(a) - 97 for a in input()]
NN = 19
BIT=[[0]*(2**NN+1) for _ in range(26)]
 
def addbit(t, i, x):
    while i <= 2**NN:
        BIT[t][i] += x
        i += i & (-i)

def getsum(t, i):
    ret = 0
    while i != 0:
        ret += BIT[t][i]
        i -= i&(-i)
    return ret

for i, a in enumerate(A):
    BIT[a][i+1] += 1

for t in range(26):
    B = [0] * (2**NN+1)
    for i in range(1<<NN):
        B[i+1] = B[i] + BIT[t][i]
    for i in range(1<<NN):
        BIT[t][i] = B[i] - B[i - (i & (-i))]

Q = int(input())
for _ in range(Q):
    a, b, c = input().rstrip().split()
    if a == "1":
        b = int(b)
        c = ord(c) - 97
        t = A[b-1]
        addbit(t, b+1, -1)
        addbit(c, b+1, 1)
        A[b-1] = c
    else:
        b, c = int(b), int(c)
        s = 0
        for t in range(26):
            s += 1 if getsum(t, c+1) - getsum(t, b) else 0
        print(s)