华为机试题 凸包

输入：

13;-3,-3;1,3;2,-4;6,1;-2,-2;4,5;1,-2;1,4;-2,3;-4,1;-1,1;2,2;1,-1

输出：

-4, 1
-2, 3
4, 5
6, 1
2, -4
-3, -3

#include<iostream>
#include<string>
#include<vector>
#include<deque>
#include<queue>
#include<stack>
#include<list>
#include<map>
#include<set>
#include<cmath>
#include<algorithm>
using namespace std;

const int maxn = 1010;
int x[maxn];
int y[maxn];

bool equal(double d1, double d2){
	d1 -= d2;
	return d1 >= -0.00001 && d1 <= 0.00001;
}

int main(){
//	freopen("test.txt", "r", stdin);

	int n, i;
	int x1 = INT_MAX;				// 横坐标最小值
	int y1;							// 左上角的纵坐标
	int x2 = INT_MIN;				// 横坐标最大值
	int y2;							// 右上角的纵坐标

	scanf("%d", &n);
	for(i = 0; i < n; ++i){
		scanf(";%d,%d", x + i, y + i);
		if(x[i] < x1){
			x1 = x[i];
			y1 = y[i];
		}else if(x1 == x[i] && y1 < y[i]){
			y1 = y[i];
		}
		if(x[i] > x2){
			x2 = x[i];
			y2 = y[i];
		}else if(x2 == x[i] && y2 < y[i]){
			y2 = y[i];
		}
	}
	
	printf("%d, %d\n", x1, y2);
	// 输出上半圈
	int cx, cy, lx = x1, ly = y1;
	double max_k, k;
	while(lx != x2){
		max_k = -INT_MIN;
		for(i = 0; i < n; ++i){
			if(x[i] <= lx){
				continue;
			}
			k = (double)(y[i] - ly) / (x[i] - lx);
			if(equal(k, max_k)){		// 斜率相同时，取距离远的
				if(x[i] > cx){
					cx = x[i];
					cy = y[i];
				}
			}else if(max_k < k){
				max_k = k;
				cx = x[i];
				cy = y[i];
			}
		}
		printf("%d, %d\n", cx, cy);
		lx = cx;
		ly = cy;
	}
	// 输出与(x2, y2)横坐标相同，纵坐标最小的点（如果有的话）
	cy = y2;
	for(i = 0; i < n; ++i){
		if(x[i] == x2 && cy < y[i]){
			cy = y[i];
		}
	}
	if(cy != y2){
		printf("%d, %d\n", x2, cy);
	}
	// 输出下半圈
	lx = x2, ly = cy;
	while(lx != x1){
		max_k = INT_MIN;
		for(i = 0; i < n; ++i){
			if(x[i] >= lx){
				continue;
			}
			k = (double)(y[i] - ly) / (x[i] - lx);
			if(equal(k, max_k)){		// 斜率相同时，选择距离远的
				if(x[i] < cx){
					cx = x[i];
					cy = y[i];
				}
			}else if(max_k < k){
				max_k = k;
				cx = x[i];
				cy = y[i];
			}
		}
		if(cx != x1){
			printf("%d, %d\n", cx, cy);
		}
		lx = cx;
		ly = cy;
	}
	// 输出与(x1, y1)横坐标相同，纵坐标最小的点（如果有的话）
	cy = y1;
	for(i = 0; i < n; ++i){
		if(x[i] == x1 && cy < y[i]){
			cy = y[i];
		}
	}
	if(cy != y1){
		printf("%d, %d\n", x1, cy);
	}
}