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Hust oj 1753 Triangular numbers(三角数）

2016-03-04 23:10 661 查看
Triangular numbers
Time Limit: 1000 MSMemory Limit: 65536 K
Total Submit: 65(43 users)Total Accepted: 43(41 users)Rating:





Special Judge: No
Description
A triangular number is the number of dots in an equilateral triangle uniformly filled with dots. For example, three dots can be arranged in a triangle; thus three is a triangular number. The n-th triangular number is the number
of dots in a triangle with n dots on a side.

Your task is to find out if a given integer is a triangular number.

Input
There are multiple test cases, processing to the end of file.

For each case:

The first line contains the single number n (1≤ n
≤ 500) — the given integer.

Output
For each case:

If the given integer is a triangular number output YES, otherwise output NO.

Sample Input
1
2
3

Sample Output
YES
NO
YES


读完了题没看明白什么叫三角数，于是找了找资料，然后就感觉这题好傻。。。

三角数即 『 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, ......』

1 = 11 + 2 = 31 + 2 + 3 = 61 + 2 + 3 + 4 = 101 + 2 + 3 + 4 + 5 = 151 + 2 + 3 + 4 + 5 + ... ...规律很明显，F
=(n^2+n)/2,上代码


#include<iostream>
using namespace std;

int main()
{
int i;
int n;
int a[501];
for(i=1;i<=500;i++)
{
a[i]=i*(i+1)/2;
}
while(cin>>n)
{
int flag=0;
for(i=1;i<=500;i++)
{
if(a[i]==n)
{
flag=1;
break;
}
}
if(flag==0)
cout<<"NO"<<endl;
else
cout<<"YES"<<endl;
}
}


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