HDU 1396 Counting Triangles

Counting Triangles

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 2565    Accepted Submission(s): 1204

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

123

 

Sample Output

1513

 

Author

JIANG, Jiefeng

 

Source

ZOJ Monthly, June 2003

 

 

注意：

1：找规律

2：正三角形与倒的三角形的规律

#include<stdio.h>int main (void){    int f[505]= {0},n,a;    f[1]=1;    f[2]=5;    f[3]=13;    f[4]=27;    f[5]=48;    for(n=6; n<=500; n++)    {        if(n%2==0)        {            f[n]=f[n-1]+(2*n-1)+(n*n-n)/2+(n*n-4*n+4)/4;        }//+(2*n-1)+(n*n-n)/2是正三角的增加规律        //(n*n-4*n+4)/4是倒三角形的增加规律        if(n%2==1)        {            f[n]=f[n-1]+(2*n-1)+(n*n-n)/2+(n*n-4*n+3)/4;        }//(n*n-4*n+3)/4是n%2==1时倒三角的增加规律    }    while(~scanf("%d",&a))    {        printf("%d\n",f[a]);    }    return 0;}