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)

import bisect
N=input()
S=list(input())
alphabet=[[] for _ in range(26)]
for i,s in enumerate(S):
    alphabet[ord(s)-ord('a')].append(i)
Q=int(input())
for _ in range(Q):
    Type,A,B=input().split()
    if Type=="1":
        A=int(A)
        s=S[A-1]
        if s==B:
            continue
        o=ord(s)-ord("a")
        alphabet[o].pop(bisect.bisect_left(alphabet[o],A-1))
        index=bisect.bisect(alphabet[B-1],A-1)
        alphabet[B-1].insert(index,A-1)
        S[A-1]=B
    else:
        A=int(A)
        B=int(B)
        ans=0
        for i in range(26):
            indexL=bisect.bisect_left(alphabet[i],A-1)
            #indexR=bisect.bisect_right(alphabet[i],B-1)
            #ans+=(indexL!=indexR)
            if indexL==len(alphabet[i]):
                continue
            ans+=(alphabet[i][indexL]<=B-1)
        print(ans)