Uva 11401 - Triangle Counting

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=2396

要注意细节

代码：

#include <iostream>

#include <cstdio>

#include <string>

#include <cstring>

#include <cmath>

#include <algorithm>



#define ll long long

using namespace std;



const int N=1000005;

ll sum[N];

int main()

{

    //freopen("data.in","r",stdin);

    memset(sum,0,sizeof(sum));

    for(ll x=4;x<N;++x)

    sum[x]=((x-1)*(x-2)/2-(x-1-(x/2)))/2;

    for(int i=1;i<N;++i)

    sum[i]=sum[i]+sum[i-1];

    int n;

    while(cin>>n)

    {

        if(n<3)break;

        cout<<sum[n]<<endl;

    }

    return 0;

}