Topcoder SRM 597 DIV 1

class LittleElephantAndString {
private:
int ch[300];
public:
int getNumber(string A, string B) {
int ans=0;
int n=A.length();
int p=n;
memset(ch,0,sizeof(ch));
for (int i=0;i<n;i++){
ch[(int)A[i]]++;
}
for (int i=0;i<n;i++){
ch[(int)B[i]]--;
}
for (int i=0;i<300;i++){
if (ch[i]!=0) return -1;
}
for (int i=n-1;i>=0;i--){
bool ok=false;
for (int j=p-1;j>=0;j--){
if (A[j]==B[i]){
ans++;
p=j;
ok=true;
break;
}
}
if (!ok) break;
}
return n-ans;
}
};