CF165C解题报告

#include<bits/stdc++.h>
using namespace std;
#define int long long
map<int,int> mp;
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int k;string s;
	cin>>k>>s;
	int n=s.size();s=' '+s;
	int sum=0;
	int ans=0;
	mp[0]=1;
	for(int i=1;i<=n;i++){
		if(s[i]=='1') sum++;
		
		ans+=mp[sum-k];
		mp[sum]++;
	}
	cout<<ans<<endl;
	return 0;
}