1 /*
2 唐代李白
3 《江夏别宋之悌》
4 楚水清若空，遥将碧海通。人分千里外，兴在一杯中。
5 谷鸟吟晴日，江猿啸晚风。平生不下泪，于此泣无穷.
6 */
7 #include <iostream>
8 #include <cstdio>
9 #include <algorithm>
10 #include <cstring>
11 #include <vector>
12 #include <utility>
13 #include <iomanip>
14 #include <string>
15 #include <cmath>
16 #include <queue>
17 #include <assert.h>
18 #include <map>
19 #include <ctime>
20 #include <cstdlib>
21 #include <stack>
22 #include <set>
23 #define LOCAL
24 const int INF = 0x7fffffff;
25 const int MAXN = 100000 + 10;
26 const int maxnode = 20000 * 2 + 200000 * 20;
27 const int MAXM = 50000 + 10;
28 const int MAX = 100;
29 using namespace std;
30 struct point{//也是vector
31 int x, y;
32 }p[MAXN], stack[MAXN];
33 int top;
34 int dis(point p1,point p2){return (p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y);}
35 //叉积，结果小于表示向量p0p1的极角大于p0p2的极角，等于则0两向量共线
36 int multi(point p1, point p2, point p0){//p0为坐标
37 return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);
38 }
39
40 int cmp(point a,point b){
41 if(multi(a,b,p[0]) > 0) return 1;
42 if(multi(a,b,p[0]) == 0 && dis(a,p[0]) < dis(b,p[0])) return 1;
43 return 0;
44 }
45 //Graham_scan凸包扫描
46 void Graham_scan(point p[],point stack[],int n){
47 int i, j, k = 0;
48 top=2;
49 point temp;
50
51 for(i=1;i<n;i++) if(p[i].y<p[k].y||((p[i].y==p[k].y)&&(p[i].x<p[k].x))) k=i;
52 swap(p[0], p[k]);
53 //按极角从小到大，距离偏短进行排序
54 sort(p + 1, p + n, cmp);
55 stack[0] = p[0];
56 stack[1] = p[1];
57 stack[2] = p[2];
58 for (int i = 3; i < n; i++){
59 while(top > 1 && multi(p[i],stack[top],stack[top-1]) >= 0)
60 top--;
61 stack[++top] = p[i];
62 }
63 }
64
65 int main(){
66 #ifdef LOCAL
67 freopen("data.txt", "r", stdin);
68 freopen("out.txt", "w", stdout);
69 #endif
70 //printf("%d", (a == c));
71 return 0;
72 }
