Counting Triangles(hd1396)

Counting Triangles

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 2506    Accepted Submission(s):
1184

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

　　分正三角形和倒三角形，

　　当长度为n时，在最低边上长度为x的正三角形，个数为n-x+1，所以总的个数为(n-x+1+1)*(n-x+1)/2

　　　　　　　　  在最低边上长度为x的倒三角形，个数为n-x*2+1(2*x<=n),所以总的个数为(n-2*x+1+1)*(n-2*x+1)/2;

 #include <iostream>
 using namespace std;
 int main()
 {
     int n,i,j;
     long long a[]={};
     for(i=;i<;i++)
     {
         for(j=;j<=i;j++)
         {
             a[i]+=(i-j++)*(i-j+)/;
             if(j*<=i)
                 a[i]+=(i-*j++)*(i-*j+)/;
         }
     }
     while(cin>>n)
         cout<<a[n]<<endl;
 }