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 OCaml (4.02.3) (judge verdict: Wrong Answer)

module S = Set.Make (struct type t = int let compare = compare end);;
let () =
    let main () =
        let n = read_line () |> int_of_string in
        let s = read_line () in
        let letter = Array.make 26 S.empty in
        for i = 0 to n - 1 do
            let code = int_of_char s.[i] - 97 in
            letter.(code) <- S.add i letter.(code)
        done;
        let q = read_int () in
        for i = 1 to q do
            Scanf.scanf " %d %d %s" (fun command a b ->
                if command = 1 then (
                    let a = a - 1 in
                    let c = int_of_char s.[a] - 97 in
                    letter.(c) <- S.remove a letter.(c);
                    let c = int_of_char b.[0] - 97 in
                    letter.(c) <- S.add a letter.(c)
                ) else (
                    let a = a - 1 in
                    let r = int_of_string b - 1 in
                    let rec loop i acc =
                        if i = 26 then acc else
                            let _,_,s = S.split (a - 1) letter.(i) in
                            let s,_,_ = S.split (r + 1) s in
                            let acc = if S.is_empty s then acc else acc + 1 in
                            loop (i + 1) acc
                    in
                    loop 0 0 |> Printf.printf "%d\n"
                )
            )
        done
    in
    main ()