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 in Python (3.4.3) (judge verdict: Runtime Error)

class SegmentTree:
    def __init__(self,l):
        nb = bin(len(l))[2:]
        b = sum([int(d) for d in nb])
        if b == 1:
            self.end_leaves = pow(2,len(nb)-1)
        else:
            self.end_leaves = pow(2,len(nb))
        self.tree = [set() for _ in range(self.end_leaves*2)]
        
        for i in range(len(l)):
            self.tree[self.end_leaves+i].add(l[i])
            
    def union(self,a):
        if a >= self.end_leaves // 2:
            self.tree[a] = self.tree[a*2] | self.tree[a*2+1]
            return self.tree[a]
        else:
            self.tree[a] = self.union(a*2) | self.union(a*2+1)
            return self.tree[a]
    def update(self,a,s):
        x = a + self.end_leaves
        self.tree[x] = set(s)
        while x > 1:
            x //= 2
            self.tree[x] = self.tree[x*2] | self.tree[x*2+1]
    def query(self,l,r):
        x = l + self.end_leaves
        y = r + self.end_leaves
        tl = set()
        tr = set()
        while y - x > 1:
            if x & 1:
                tl = tl | self.tree[x]
                x += 1
            if y & 0:
                tr = self.tree[y] | tr
                y -= 1
            x >>= 1
            y >>= 1
        if y - x == 0:
            print(len(tl|tr|self.tree[x]))
        else:
            print(len(tl|tr|self.tree[x]|self.tree[y]))
            
            

N = int(input())
S = list(input())
st = SegmentTree(S)
st.union(1)
Q = int(input())
for i in range(Q):
    q = input().split()
    if q[0] == '1':
        st.update(int(q[1])-1,q[2])
    else:
        st.query(int(q[1])-1,int(q[2])-1)