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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <string.h>
#include <stdbool.h>

int main() {
    char str[500001] = {};
    int n, q;
    int type, i, l, r, count;
    char c;
    int abc[26] = {};
    bool strlong = false;
    bool finish = false;
    scanf("%d", &n);
    scanf("%s", str);
    scanf("%d", &q);
    for (int k = 0; k < q; k++){
        scanf("%d", &type);
        if (type == 1) {
            scanf("%d %c", &i ,&c);
            str[i - 1] = c;
        }
        else {
            memset(abc, 0, sizeof(abc));
            count = 0;
            finish = strlong = false;
            scanf("%d %d", &l, &r);
            if (r - l > 26)
                strlong = true;
            for (int i = l; i < r + 1; i++) {
                for (int j = 0; j < 26; j++) {
                    if (str[i - 1] == (char)('a' + j)) {
                        abc[j] = 1;
                        break;
                    }
                }
                if (strlong) {
                    for (int i = 0; i < 26; i++) {
                        if (abc[i])
                            count++;
                    }
                    if (count == 26) {
                        printf("26\n");
                        finish = true;
                        break;
                    }
                }
            }
            if (!finish) {
                for (int i = 0; i < 26; i++) {
                    if (abc[i])
                        count++;
                }
                printf("%d\n", count);
            }
        }
    }
    
    return 0;
}