K - Table

SDUT 2022 Spring Individual Contest(for 21) - 6 - Virtual Judge

There are 4 bars, possibly, having different lengths. Can they be used as the legs of the table, such that:

• The legs stay vertically in the vertices of some rectangle;
• The surface of the table, possibly, sloping, touches all four legs?

Input

The input contains 4 integers a_1a1​, a_2a2​, a_3a3​, a_4a4​ (1 le a_i le 10^91≤ai​≤109) — the lengths of the bars.

Output

Output "YES" or "NO", depending on it is possible to make a table with the given design or not.

Sample 1

1 1 1 1

YES

Sample 2

1 5 1 5

YES

Sample 3

1 3 2 2

YES

Sample 4

9 5 11 8

NO

题意：给定一个桌子的四个桌脚的长度，判断这四个桌脚能否恰好保证支撑起这个桌子（即保证桌面是一个平面）。 

#include
using namespace std;
int main()
{
    int a[5];
    for(int i=0;i<4;i++)
    {
        scanf("%d",&a[i]);
    }
    sort(a,a+4);
    if(a[1]-a[0]==a[3]-a[2])
       printf("YESn");
    else
        printf("NOn");
}

别人的题解：

设这四根桌脚的长度分别为 a0,a1,a2,a3。a0,a1,a2,a3 （从小到大排列），如果 ABCDABCD 为一平面，则必须满足：

|DM|=|CN|⇔a3-a1=a2-a0

 面CBAD是一个面--->CB==AD-->三角形CBN与三角形DMA全等