HDUOJ-Counting Triangles

Counting Triangles

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others) Total Submission(s): 1882    Accepted Submission(s): 898

Problem Description

Given an equilateral triangle with n the length of its side, program to count how many triangles in it.

Input

The length n (n <= 500) of the equilateral triangle's side, one per line. process to the end of the file

Output

The number of triangles in the equilateral triangle, one per line.

Sample Input

1 2 3

Sample Output

1 5 13

Author

JIANG, Jiefeng

Source

http://acm.hdu.edu.cn/showproblem.php?pid=1396

Recommend

Ignatius.L

规律在这：

http://mathworld.wolfram.com/TriangleTiling.html

代码：

#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
    int n;
    int sum;
    while(cin>>n)
    {
        sum=n*(n+2)*(2*n+1);
        if(n&1)    sum--;
        printf("%d\n",sum/8);
    }
    return 0;
}