hdu 1392 模板凸包

最新推荐文章于 2025-08-03 13:26:02 发布

HZXPH

最新推荐文章于 2025-08-03 13:26:02 发布

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分类专栏：计算几何文章标签： p2p

本文链接：https://blog.youkuaiyun.com/HZXPH/article/details/6656966

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本文记录了一次解决计算几何中凸包问题的经历，通过不断调试最终发现只需特殊处理两点情况即可通过测试。文章分享了完整的代码实现过程。

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这真的是太囧了，我差点就

这样了，明明就是一道模板题，可怎么改都错，交了十几二十次还是WA……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………............................................................................................................................................……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………一天早上就过去了……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………吃完饭当然还是不甘心，突然在用别人的代码上看到，当只有两点的时候，有要算一边就好了，这时我就

这样了，太囧了…………结果就这样过了

烦，不解释，不写了

#include<iostream>
#include<vector>
#include<algorithm>
#include<stack>
#include<cmath>

using namespace std;

class cor{
public:
	int x, y;
};

cor start;

bool drection(cor& p0,cor& p1,cor& p2){
	int x1 = p1.x-p0.x;
	int y1 = p1.y-p0.y;
	int x2 = p2.x-p0.x;
	int y2 = p2.y-p0.y;
	if(x2*y1-x1*y2 > 0)
		return true;
	return false;
}

bool cmp(cor& lhs,cor& rhs){
	return drection(start,rhs,lhs);
}

double calc(cor p1,cor p2){
	double a = pow((double)(p1.x-p2.x),2);
	double b = pow((double)(p1.y-p2.y),2);
	return sqrt(a+b);
}

int main()
{
	int ntree;
	while(cin >>ntree && ntree){
		vector<cor> trees;
		stack<cor> ch;
		cin >>start.x >>start.y;
		for(int i = 1;i < ntree;i++){
			cor p;
			cin >>p.x >>p.y;
			if(p.y < start.y){
				trees.push_back(start);
				start = p;
			}
			else if(p.y == start.y && p.x <start.x){
				trees.push_back(start);
				start = p;
			}
			else
			    trees.push_back(p);
		}
		if(ntree == 1){
			printf("0.00\n");
			continue;
		}
		if(ntree == 2){
			printf("%.2lf\n",calc(start,trees[0]));
			continue;
		}
		sort(trees.begin(),trees.end(),cmp);
		ch.push(start);
		ch.push(trees[0]);
		ch.push(trees[1]);
		for(vector<cor>::size_type i = 2;i < trees.size();i++){
			cor p0,p1,p2;
			p1 = ch.top();
			ch.pop(); p0 = ch.top(); ch.push(p1);//取栈顶下一个元素
			p2 = trees[i];
			while(drection(p0,p1,p2)){
				ch.pop();
				p1 = ch.top();
				ch.pop(); p0 = ch.top(); ch.push(p1);//取栈顶下一个元素
			}
			ch.push(p2);
		}
		double len = 0.0;
		cor p1,p2; ch.push(start);
		p1 = ch.top(); p2 = p1;
		stack<cor>::size_type k = ch.size();
		for(stack<cor>::size_type i = 1;i < k;i++){
			ch.pop();
			p2 = ch.top();
			len += calc(p1,p2);
			p1 = p2;
		}
		printf("%.2lf\n",len);
	}
	return 0;
}