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: Wrong Answer)

from bisect import bisect_left,bisect_right,insort
N = int(input())
S = input()
Q = int(input())
C = [0]
X = set()
D = dict()
D2 = dict()# to be removed
D3 = dict()# to be added 
for i in range(97,97+26):
    D[chr(i)] = []
    D2[chr(i)] = []
    D3[chr(i)] = []
for i in range(N):
    D[S[i]].append(i+1)
for i in range(Q):
    t,l,r = input().split()
    if t == str(1):
        k = int(l)
        c = r
        insort(D2[S[k-1]],k)
        insort(D3[c],k)
        #D2[S[k-1]].append(k)
        #D3[c].append(k)
        continue
    l = int(l)
    r = int(r)
    ans = 0
    for i in range(97,97+26):
        X = D[chr(i)]
        X2 = D2[chr(i)]
        X3 = D3[chr(i)]
        if bisect_right(X,r)-bisect_left(X,l) + bisect_right(X3,r)- bisect_left(X3,l) -bisect_right(X2,r)+bisect_left(X2,l)> 0:
            ans += 1
    print(ans)