B. Mahmoud and a Triangle

Mahmoud has n line segments, the i-th of them has length a_i. Ehab challenged him to use exactly 3 line segments to form a non-degenerate triangle. Mahmoud doesn’t accept challenges unless he is sure he can win, so he asked you to tell him if he should accept the challenge. Given the lengths of the line segments, check if he can choose exactly 3 of them to form a non-degenerate triangle.

Mahmoud should use exactly 3 line segments, he can’t concatenate two line segments or change any length. A non-degenerate triangle is a triangle with positive area.

The first line contains single integer n (3 ≤ n ≤ 10⁵) — the number of line segments Mahmoud has.

The second line contains n integers a₁, a₂, …, a_n (1 ≤ a_i ≤ 10⁹) — the lengths of line segments Mahmoud has.

In the only line PRint “YES” if he can choose exactly three line segments and form a non-degenerate triangle with them, and “NO” otherwise.

51 5 3 2 4Output
YESInput
34 1 2Output
NONote
For the first example, he can use line segments with lengths 2, 4 and 5 to form a non-degenerate triangle.
题意： 给一组数，从中挑选三个数字是否为三角形（只要有一组符合就可以 解析： 利用两边之和第三边就可以
#include<stdio.h>#include<string.h>#include<algorithm>using namespace std;#define N 100005int arr[N]; bool cmp(int x,int y){    return x > y;} int main(){    int n;    while(~scanf("%d",&n)) {        bool flag = false;        for(int i = 0;i < n; i++) {            scanf("%d",&arr[i]);        }        sort(arr,arr+n,cmp);        for(int i = 0;i < n-2; i++) {            if(arr[i] < arr[i+1]+arr[i+2]) {                printf("YES/n");                flag = true;                break;            }        }        if(!flag) {            printf("NO/n");        }    }return 0;}