LeetCode Weekly Contest 32 解题报告

1 class Solution {
2 public:
3     /*计算两点之间距离*/
4     static int dis(Point p1,Point p2)
5     {
6         return (p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y);
7     }
8     /*利用×乘 计算三点之间关系 0：共线 1：依次成顺时针 2：依次成逆时针*/
9     static int orientation(Point p1,Point p2,Point p3)
10     {
11         int val=(p3.y-p1.y)*(p2.x-p1.x)-(p3.x-p1.x)*(p2.y-p1.y);
12         if(val==0)
13             return 0;
14         else
15             return val>0?2:1;
16     }
17     /*将点排序 采用结构体进行排序 第一次见*/
18     struct pointsComparator
19     {
20         Point p0;/*基准点*/
21         bool operator() (const Point& p1,const Point&  p2)
22         {
23             int val=orientation(p0,p1,p2);
24             if(val==0)
25                 return dis(p0,p1)<=dis(p0,p2);
26             else
27                 return val==2;
28         }
29         pointsComparator(Point p): p0(p){}
30     };
31     vector<Point> outerTrees(vector<Point>& points) {
32         int n=points.size();
33         if(n<=3)
34             return points;
35         int ymin=points[0].y,minlo=0;/*找y坐标最小的点，记录其下标*/
36         for(int i=1;i<n;++i)
37         {
38             if(points[i].y<ymin||(points[i].y==ymin&&points[i].x<points[minlo].x))
39                 ymin=points[i].y,minlo=i;
40         }
41         Point tem=points[0];
42         points[0]=points[minlo];
43         points[minlo]=tem;
44         Point p0=points[0];
45         sort(points.begin(),points.end(),pointsComparator(p0));
46
47
48         Point pn = points.back();
49         if (orientation(p0, points[1], pn) != 0) {//非所有点都共线
50             int idx = n-1;
51             while (orientation(p0, points[idx], pn) == 0) {//找到
52                 idx--;
53             }
54             reverse(points.begin() + idx + 1, points.end());//调序？？为啥
55         }
56
57
58         vector<Point> vertices;
59         vertices.push_back(points[0]);
60         vertices.push_back(points[1]);
61         vertices.push_back(points[2]);
62         for(int i=3;i<n;++i)
63         {
64             while(orientation(vertices[vertices.size()-2],vertices.back(),points[i])==1)
65                 vertices.pop_back();
66             vertices.push_back(points[i]);
67         }
68         return vertices;
69     }
70 };