UVa 11401 - Triangle Counting

Problem G

Triangle Counting

Input: Standard Input

Output: Standard Output

 

 

You are given n rods of length 1, 2…, n. You have to pick any 3 of them & build a triangle. How many distinct triangles can you make? Note that, two triangles will be considered different if they have at least 1 pair of arms with different length.

 

Input

 

The input for each case will have only a single positive integer n (3<=n<=1000000). The end of input will be indicated by a case with n<3. This case should not be processed.

 

Output

 

For each test case, print the number of distinct triangles you can make.

 

Sample Input                                                  Output for Sample Input

5 8 0

3 22

 

 

#include<iostream>
#include<cstdio>

using namespace std;

const int maxn=1000010;

long long num[maxn];

int main(){

    //freopen("input.txt","r",stdin);

    num[3]=0;
    for(long long i=4;i<maxn;i++)       //这里不能用int，否则UVa上WA

        num[i]=num[i-1]+((i-1)*(i-2)/2-(i-1)/2)/2;
    int n;
    while(cin>>n){
        if(n<3)
            break;
        cout<<num[n]<<endl;
    }
    return 0;
}