HDU 5135 Little Zu Chongzhi's Triangles（貪心）

題解：

貪心從大到小排序加遍歷，三個一起遍歷從大到小，如果滿足三角形條件都可以加上答案。

#include <algorithm>
#include  <iostream>
#include   <cstdlib>
#include   <cstring>
#include    <cstdio>
#include    <string>
#include    <vector>
#include    <bitset>
#include     <stack>
#include     <cmath>
#include     <deque>
#include     <queue>
#include      <list>
#include       <set>
#include       <map>
#define mem(a, b) memset(a, b, sizeof(a))
#define pi acos(-1)
using namespace std;
typedef long long ll;
const int  inf = 0x3f3f3f3f;
const int maxn = 15;

double line[maxn];

int main(){
	int n;
	while(scanf("%d", &n), n){
		for(int i = 0l; i < n; i++){
			scanf("%lf", &line[i]);
		}
		sort(line, line+n);
		double ans = 0;
		for(int i = n-3; i >= 0;){
			if(line[i]+line[i+1] > line[i+2]){
				double p = (line[i]+line[i+1]+line[i+2])/2.0;
				ans += sqrt(p*(p-line[i+1])*(p-line[i])*(p-line[i+2]));
				i -= 3;
			}
			else{
				i--;
			}
		}
		printf("%.2lf\n", ans);
	}
}