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 Go (1.6) (judge verdict: Wrong Answer)

package main

import (
	"fmt"
	"sort"
)

func insert(a []int, x int) []int {
	i := sort.SearchInts(a, x)
	return append(append(a[:i], x), a[i:]...)
}

func remove(a []int, x int) []int {
	i := sort.SearchInts(a, x)
	if i < len(a)-1 {
		return append(a[:i], a[i+1:]...)
	}
	return a[:i]
}

func main() {
	var n, q int
	var str string
	fmt.Scan(&n, &str, &q)

	s := []byte(str)
	abc := [26][]int{}
	for i := 0; i < n; i++ {
		c := s[i] - 'a'
		abc[c] = append(abc[c], i)
	}

	for k := 0; k < q; k++ {
		var t int
		fmt.Scan(&t)

		if t == 1 {
			var i int
			var a string
			fmt.Scan(&i, &a)
			i--

			c := s[i] - 'a'
			abc[c] = remove(abc[c], i)
			s[i] = a[0]
			c = s[i] - 'a'
			abc[c] = insert(abc[c], i)
		} else {
			var l, r int
			fmt.Scan(&l, &r)
			l--

			cnt := 0
			for c := 0; c < 26; c++ {
				i := sort.SearchInts(abc[c], l)
				if i < len(abc[c]) && abc[c][i] < r {
					cnt++
				}
			}
			fmt.Println(cnt)
		}

	}
}