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: Accepted)

class SegmentTree:
    def __init__(self,orig,func,unit):
        _len= len(orig)
        self.func = func
        self.size = 1 << (_len-1).bit_length()
        self.tree = [unit] * self.size + orig + [unit] *(self.size-_len)
        self.unit = unit
        
        for i in range(self.size -1,0,-1):
            self.tree[i] = func(self.tree[i*2], self.tree[i*2+1])
            
    def update(self, i, v):
        i+=self.size
        self.tree[i] = v
        while i:
            i//=2
            self.tree[i]=self.func(self.tree[i*2],self.tree[i*2+1])
    
    def find(self,l,r):
        l+=self.size
        r+=self.size
        ret=self.unit
        while l<r:
            if l&1:
                ret = self.func(ret,self.tree[l])
                l+=1
            if r&1:
                r-=1
                ret=self.func(ret,self.tree[r])
            l//=2
            r//=2
        return ret
      
import sys
input = sys.stdin.readline
from operator import or_

input()
seg = SegmentTree([1 << ord(x) - 97 for x in input()[:-1]], or_, 0)
ans = []
for _ in range(int(input())):
  f, x, y = input().split()
  if f == "1":
    seg.update(int(x) - 1, 1 << ord(y) - 97)
  else:
    ans.append(bin(seg.find(int(x) - 1, int(y))).count("1"))
print(*ans)