Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline
n = int(input())
s = input()
q = int(input())
for i in range(q):
  que = input().split()
  if que[0] == '1':
    na,mu = que[1],que[2]
    na = int(na)
    s = s[:na-1] + mu + s[na:]
  else:
    na,mu = que[1],que[2]
    na,mu = int(na),int(mu)
    c = set(s[na-1:mu])
    print(len(c))

Fixed submission:
import sys
readline = sys.stdin.readline

from bisect import bisect_left, insort_left

def main():
    n = int(readline())
    s = list(readline().rstrip())
    q = int(readline())
    
    chk_abc = [[] for i in range(26)]
    for i, si in enumerate(s):
        ci = ord(si) - 97
        chk_abc[ci].append(i)
        
    ans = []
    for _ in range(q):
        cmd, i, j = readline().rstrip().split()
        i = int(i) - 1
        
        if cmd == "1":
            if s[i] == j:
                continue
            c1 = ord(s[i]) - 97
            prev = chk_abc[c1]
            c2 = ord(j) - 97
            prev.pop(bisect_left(prev, i))
            s[i] = j
            insort_left(chk_abc[c2], i)
            
        else:
            j = int(j) - 1
            num = 0
            for chk in chk_abc:
                le = len(chk)
                k = bisect_left(chk, i, 0, le)
                if k == le:
                    continue
                if i <= chk[k] <= j:
                    num += 1
            ans.append(num)

    print(*ans, sep="\n")

if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline
n = int(input())
s = list(input())
q = int(input())
for i in range(q):
  que = input().split()
  if que[0] == '1':
    na,mu = que[1],que[2]
    na = int(na)
    s[na-1] = mu
  else:
    na,mu = que[1],que[2]
    na,mu = int(na),int(mu)
    c = set(s[na-1:mu])
    print(len(c))

Fixed submission:
import sys
readline = sys.stdin.readline

from bisect import bisect_left, insort_left

def main():
    n = int(readline())
    s = list(readline().rstrip())
    q = int(readline())
    
    chk_abc = [[] for i in range(26)]
    for i, si in enumerate(s):
        ci = ord(si) - 97
        chk_abc[ci].append(i)
        
    ans = []
    for _ in range(q):
        cmd, i, j = readline().rstrip().split()
        i = int(i) - 1
        
        if cmd == "1":
            if s[i] == j:
                continue
            c1 = ord(s[i]) - 97
            prev = chk_abc[c1]
            c2 = ord(j) - 97
            prev.pop(bisect_left(prev, i))
            s[i] = j
            insort_left(chk_abc[c2], i)
            
        else:
            j = int(j) - 1
            num = 0
            for chk in chk_abc:
                le = len(chk)
                k = bisect_left(chk, i, 0, le)
                if k == le:
                    continue
                if i <= chk[k] <= j:
                    num += 1
            ans.append(num)

    print(*ans, sep="\n")

if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
s = list(input())
q = int(input())
for i in range(q):
  que = input().split()
  if que[0] == '1':
    s[int(que[1])-1] = que[2]
  else:
    c = set(s[int(que[1])-1:int(que[2])])
    print(len(c))

Fixed submission:
import sys
readline = sys.stdin.readline

from bisect import bisect_left, insort_left

def main():
    n = int(readline())
    s = list(readline().rstrip())
    q = int(readline())
    
    chk_abc = [[] for i in range(26)]
    for i, si in enumerate(s):
        ci = ord(si) - 97
        chk_abc[ci].append(i)
        
    ans = []
    for _ in range(q):
        cmd, i, j = readline().rstrip().split()
        i = int(i) - 1
        
        if cmd == "1":
            if s[i] == j:
                continue
            c1 = ord(s[i]) - 97
            prev = chk_abc[c1]
            c2 = ord(j) - 97
            prev.pop(bisect_left(prev, i))
            s[i] = j
            insort_left(chk_abc[c2], i)
            
        else:
            j = int(j) - 1
            num = 0
            for chk in chk_abc:
                le = len(chk)
                k = bisect_left(chk, i, 0, le)
                if k == le:
                    continue
                if i <= chk[k] <= j:
                    num += 1
            ans.append(num)

    print(*ans, sep="\n")

if __name__ == "__main__":
    main()