哈尔滨理工大学软件学院ACM程序设计全国邀请赛（网络同步赛）E 666 By Assassin 坑点水题

Description CA loves “6” very much. Now CA has a string S which consists of N digits. Now, she wonders that there are how many non-empty strings are substring of S and only contain number “6”. Input First line contains T denoting the number of testcases. T testcases follow. Each testcase contains a integer in the first line, denoting N, the length of string S. The second line is a string whose length is N. 1≤T≤10, 2≤N≤200000 Output For each test case, output answer. Sample Input 2
3
616
3
166

Sample Output
2
3

讲真这种题真不应该写个博客，但是重点就是没有想到用int
类型计算得到long long的过程中可能会爆炸，是我太菜了，发个博记录下。

#include<bits/stdc++.h>#define input freopen("input.txt","r",stdin)using namespace std;int main(){    //freopen("input.txt","r",stdin);    int n,i,j,t,start,end,flag;    long long sum;    string s;    scanf("%d",&t);        while(t--){            sum=0;            scanf("%d",&n);            cin>>s;            s+='0';            start=end=0;            for(flag=0,i=0;i<=n;i++){                if(flag==0&&s[i]=='6'){                    flag=1;                    start=i;                }                else if(flag==1&&s[i]!='6'){                    flag=0;                    sum+=(long long)((1+(long long)(i-start))*(i-start)/2);  //就是这！                }            }            cout<<sum<<endl;        }    return 0;}