题意翻译
给定一个数n，问你是否存在一个整数i，满足i*(i+1)/2=n。
若存在，输出"YES",否则输出"NO".
1<=n<=500
Translated by @稀神探女
题目描述
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 nn -th triangular number is the number of dots in a triangle with nndots on a side. 
. You can learn more about these numbers from Wikipedia (http://en.wikipedia.org/wiki/Triangular\_number).
Your task is to find out if a given integer is a triangular number.
输入输出格式
输入格式：
The first line contains the single number nn ( 1<=n<=5001<=n<=500 ) — the given integer.
输出格式：
If the given integer is a triangular number output YES, otherwise output NO.
输入输出样例
#include<cstdio> #include<cstring> #include<iostream> #include<algorithm> using namespace std; int n; int main(){ scanf("%d",&n); for(int i=1;i<=n;i++) if(i*i+i==2*n){ cout<<"YES"; return 0; } cout<<"NO"; }