[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

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#include<stdio.h>

unsigned long long int s[1000005]={0};

int main(){

    long long int i,n;

    for(i=4;i<=1000000;i++){

        s[i]=s[i-1];

        n=i/2;

        s[i]+=n*(n-1)/2;

        n=i-n-1;

        s[i]+=n*(n-1)/2;

    }

    while(scanf("%lld",&n)!=EOF && n>2){

        printf("%llu\n",s[n]);

    }

}