Buggy python submission (verdict: Runtime Error):
import bisect

N=int(input())
S=list(input())
Q=int(input())

alphabet="abcdefghijklmnopqrstuvwxyz"
bag={l:[] for l in alphabet}
for i in range(N):
    bag[S[i]].append(i+1)
#print(bag)

for i in range(Q):
    Type,a,b=input().split()
    if Type=='1':
        if S[a-1]!=b:
            a=int(a)
            bag[S[a-1]].remove(a)
            S[a-1]=b
            bisect.insort(bag[b],a)
    else:
        cnt=0
        a,b=int(a),int(b)
        for l in alphabet:
            bl=len(bag[l])
            if bl>0:
                left=bisect.bisect_left(bag[l],a)
                if left!=bl and bag[l][left]<=b:
                        cnt+=1
        print(cnt)

Fixed submission:
import bisect

N=int(input())
S=list(input())
Q=int(input())

alphabet="abcdefghijklmnopqrstuvwxyz"
bag={l:[] for l in alphabet}
for i in range(N):
    bag[S[i]].append(i+1)
#print(bag)

for i in range(Q):
    Type,a,b=input().split()
    if Type=='1':
        a=int(a)
        if S[a-1]!=b:
            bag[S[a-1]].remove(a)
            S[a-1]=b
            bisect.insort(bag[b],a)
    else:
        cnt=0
        a,b=int(a),int(b)
        for l in alphabet:
            bl=len(bag[l])
            if bl>0:
                left=bisect.bisect_left(bag[l],a)
                if left!=bl and bag[l][left]<=b:
                        cnt+=1
        print(cnt)

Buggy python submission (verdict: Time Limit Exceeded):
import bisect

import sys
input = sys.stdin.readline

N=int(input())
S=list(input())
Q=int(input())

alphabet="abcdefghijklmnopqrstuvwxyz"
bag={l:[] for l in alphabet}
for i in range(N):
    bag[S[i]].append(i+1)
#print(bag)

for i in range(Q):
    Type,a,b=input().split()
    if Type=='1':
        a=int(a)
        bag[S[a-1]].remove(a)
        S[a-1]=b
        bisect.insort(bag[b],a)
    else:
        cnt=0
        a,b=int(a),int(b)
        for l in alphabet:
            bl=len(bag[l])
            if bl>0:
                left=bisect.bisect_left(bag[l],a)
                if left!=bl and bag[l][left]<=b:
                    cnt+=1
        print(cnt)

Fixed submission:
import bisect

N=int(input())
S=list(input())
Q=int(input())

alphabet="abcdefghijklmnopqrstuvwxyz"
bag={l:[] for l in alphabet}
for i in range(N):
    bag[S[i]].append(i+1)
#print(bag)

for i in range(Q):
    Type,a,b=input().split()
    if Type=='1':
        a=int(a)
        if S[a-1]!=b:
            bag[S[a-1]].remove(a)
            S[a-1]=b
            bisect.insort(bag[b],a)
    else:
        cnt=0
        a,b=int(a),int(b)
        for l in alphabet:
            bl=len(bag[l])
            if bl>0:
                left=bisect.bisect_left(bag[l],a)
                if left!=bl and bag[l][left]<=b:
                        cnt+=1
        print(cnt)

Buggy python submission (verdict: Time Limit Exceeded):
import bisect

N=int(input())
S=list(input())
Q=int(input())

alphabet="abcdefghijklmnopqrstuvwxyz"
bag={l:[] for l in alphabet}
for i in range(N):
    bag[S[i]].append(i+1)
#print(bag)

for i in range(Q):
    Type,a,b=input().split()
    if Type=='1':
        a=int(a)
        bag[S[a-1]].remove(a)
        S[a-1]=b
        bisect.insort(bag[b],a)
    else:
        cnt=0
        a,b=int(a),int(b)
        for l in alphabet:
            bl=len(bag[l])
            if bl>0:
                left=bisect.bisect_left(bag[l],a)
                if left!=bl and bag[l][left]<=b:
                    cnt+=1
        print(cnt)

Fixed submission:
import bisect

N=int(input())
S=list(input())
Q=int(input())

alphabet="abcdefghijklmnopqrstuvwxyz"
bag={l:[] for l in alphabet}
for i in range(N):
    bag[S[i]].append(i+1)
#print(bag)

for i in range(Q):
    Type,a,b=input().split()
    if Type=='1':
        a=int(a)
        if S[a-1]!=b:
            bag[S[a-1]].remove(a)
            S[a-1]=b
            bisect.insort(bag[b],a)
    else:
        cnt=0
        a,b=int(a),int(b)
        for l in alphabet:
            bl=len(bag[l])
            if bl>0:
                left=bisect.bisect_left(bag[l],a)
                if left!=bl and bag[l][left]<=b:
                        cnt+=1
        print(cnt)

Buggy python submission (verdict: Runtime Error):
import bisect

N=int(input())
S=list(input())
Q=int(input())
L=[[] for i in range(150)]

for i in range(N):
    L[ord(S[i])].append(i)

#print(L)

for i in range(Q):
    
    Type,q1,q2=map(str,input().split())
    if Type=='1':
        q1=int(q1)-1
        L[ord(S[q1])].remove(q1)
        L[ord(q2)].append(q1)
        L[ord(q2)]=sorted(L[ord(q2)])
    else:
        q1,q2=int(q1)-1,int(q2)-1
        cnt=0
        for j in range(97,123):
            if len(L[j])!=0:
                L[j]=sorted(L[j])
                n=bisect.bisect_left(L[j],q1)
                #print(j,n)
                if n<len(L[j]) and L[j][n]<=q2:
                    cnt+=1
                    #print(str(j),'<')
        print(cnt)

Fixed submission:
import bisect

N=int(input())
S=list(input())
Q=int(input())

alphabet="abcdefghijklmnopqrstuvwxyz"
bag={l:[] for l in alphabet}
for i in range(N):
    bag[S[i]].append(i+1)
#print(bag)

for i in range(Q):
    Type,a,b=input().split()
    if Type=='1':
        a=int(a)
        if S[a-1]!=b:
            bag[S[a-1]].remove(a)
            S[a-1]=b
            bisect.insort(bag[b],a)
    else:
        cnt=0
        a,b=int(a),int(b)
        for l in alphabet:
            bl=len(bag[l])
            if bl>0:
                left=bisect.bisect_left(bag[l],a)
                if left!=bl and bag[l][left]<=b:
                        cnt+=1
        print(cnt)