hdu 6512 Triangle

Problem Description

After Xiaoteng took a math class, he learned a lot of different shapes, but Xiaoteng's favorite triangle is because he likes stable shapes, just like his style. 

After the Xiaoxun knew it, he wanted to give a triangle as a gift to Xiaoteng. He originally planned to do one, but he was too tired. So he decided to bring some wooden sticks to Xiaoteng and let Xiaoteng make a triangle himself. 

One day, Xiaoxun brought n sticks to Xiaoteng. Xiaoteng wanted to try to use three of them to form a triangle, but the number is too much, Xiaoteng stunned, so he can only ask for your help.

 

Input

There are mutiple test cases.

Each case starts with a line containing a integer  n(1≤n≤5×106)  which represent the number of sticks and this is followed by n positive intergers(smaller than 231−1) separated by spaces.

 

Output

YES or NO for each case mean Xiaoteng can or can't use three of sticks to form a triangle.

 

Sample Input

4 1 2 3 4

 

Sample Output

YES

 

Source

2019中山大学程序设计竞赛（重现赛）

 

很水的题，原来输入的数据是排好序的，怪不得加上排序就超时了，对于排好序的，只需要判断相邻两个的和是否大于第三个就可以了，想一想画面，很好理解。

代码：

#include <iostream>
#include <cstdlib>
#include <cstdio>

using namespace std;
int n,a[5000000];
int main() {
    while(~scanf("%d",&n)) {
        for(int i = 0;i < 2 && i < n;i ++) {
            scanf("%d",&a[i]);
        }
        int flag = 0;
        for(int i = 2;i < n;i ++) {
            scanf("%d",&a[i]);
            if(flag) continue;
            if(a[i - 2] > a[i] - a[i - 1]) {
                flag = 1;
            }
        }
        puts(flag ? "YES" : "NO");
    }
}