TOJ 1809.Playground（构成多边形条件）

题目链接：http://acm.tju.edu.cn/toj/showp1809.html

1809.    Playground

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Time Limit: 1.0 Seconds    Memory Limit: 65536K
Total Runs: 3056    Accepted Runs: 770

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George has K ≤ 20 steel wires shaped in the form of half-circles, with radii a ₁, a ₂, ... , a _K. They can be soldered (connected) at the ends, in any angle. Is it possible for George to make a closed shape out of these wires? He does not have to use all the wires.

The wires can be combined at any angle, but may not intersect. Beware of floating point errors.

Input specifications

Each data set consists of a number 0 < K ≤ 20 on a line by itself, followed by a line of K space-separated numbers a_i. Each number is in the range 0 < a_i < 10⁷, and has at most 3 digits after the decimal point. The input will be terminated by a zero on a line by itself.

Output specifications

For each test case, there should be one word on a line by itself: "YES" if it is possible to make a simple connected figure out of the given arcs, and "NO" if it isn't.

Sample Input

1
4.000
2
1.000 1.000
3
1.455 2.958 4.424
7
1.230 2.577 3.411 2.968 5.301 4.398 6.777
0

Sample Output

NO
YES
NO
YES

Source: Nordic Collegiate Contest 2005

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与构成多边形的条件差不多，对于半圆，要注意的是两个半圆也是可以闭合的，还有就是等于也是可以的。

#include 
#include 
using namespace std;
int main(){
	double wire[21];
	int n;
	while(~scanf("%d",&n),n){
		bool flag=false;
		for(int i=0;i