Codeforces Round #502 (in memory of Leopoldo Taravilse, Div. 1 + Div. 2) B. The Bits

1. link:http://codeforces.com/contest/1017/problem/B
2. AC code:

找呀找呀找规律

#include<iostream>
using namespace std;
int main(){
    int n,c=0,d=0;long long ans=0;
    string a,b;cin>>n>>a>>b;
    for(int i=0;i<n;i++)
        if(a[i]=='1'&&b[i]=='0')c++,d++;
        else if(a[i]=='1'&&b[i]=='1')d++;
    for(int i=0;i<n;i++)
        if(a[i]=='0'){
            if(b[i]=='1')ans+=c;
            else ans+=d;
        }
    cout<<ans<<endl;
}