【HDOJ】3285 Convex Hull of Lattice Points

凸包模板题目。

 1 /* 3285 */
 2 #include <iostream>
 3 #include <cstdio>
 4 #include <cstring>
 5 #include <cmath>
 6 #include <algorithm>
 7 using namespace std;
 8 
 9 #define MAXN 55
10 
11 typedef struct {
12     int x, y;
13 } Point_t;
14 
15 Point_t points[MAXN];
16 Point_t stack[MAXN];
17 int top;
18 
19 void output(int);
20 
21 double dist(Point_t a, Point_t b) {
22     return sqrt(1.0*(a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
23 }
24 
25 int dist2(Point_t a, Point_t b) {
26     return (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y);
27 }
28 
29 int cross(Point_t a, Point_t b, Point_t c) {
30     return (b.x-a.x)*(c.y-a.y) - (c.x-a.x)*(b.y-a.y);
31 }
32 
33 bool comp(Point_t a, Point_t b) {
34     int m = cross(points[0], a, b);
35     return m>0 || (m==0 && dist2(points[0], a)<dist2(points[0], b));
36 }
37 
38 void Graham(int n) {
39     Point_t p;
40     int i, j, k;
41     
42     p = points[0];
43     k = 0;
44     for (i=1; i<n; ++i) {
45         if (points[i].x<p.x || (points[i].x==p.x && points[i].y<p.y)) {
46             p = points[i];
47             k = i;
48         }
49     }
50     points[k] = points[0];
51     points[0] = p;
52     
53     sort(points+1, points+n, comp);
54     
55     stack[0] = points[0];
56     stack[1] = points[1];
57     top = 1;
58     
59     for (i=2; i<n; ++i) {
60         while(top && cross(stack[top-1], stack[top], points[i])<=0)
61             --top;
62         stack[++top] = points[i];
63     }
64 }
65 
66 int main() {
67     int t, case_n;
68     int n;
69     int i, j, k;
70     Point_t p;
71     
72 #ifndef ONLINE_JUDGE
73     freopen("data.in", "r", stdin);
74 #endif
75 
76     scanf("%d", &t);
77     while (t--) {
78         scanf("%d %d", &case_n, &n);
79         for (i=0; i<n; ++i)
80             scanf("%d %d", &points[i].x, &points[i].y);
81         Graham(n);
82         printf("%d %d\n", case_n, top+1);
83         p = stack[0];
84         k = 0;
85         for (i=1; i<=top; ++i) {
86             if (stack[i].y>p.y || (stack[i].y==p.y && stack[i].x<p.x)) {
87                 p = stack[i];
88                 k = i;
89             }
90         }
91         for (i=k; i>=0; --i)
92             printf("%d %d\n", stack[i].x, stack[i].y);
93         for (i=top; i>k; --i)
94             printf("%d %d\n", stack[i].x, stack[i].y);
95     }
96 
97     return 0;
98 }

 

posted on 2015-01-03 22:12  Bombe  阅读(234)  评论(0)  编辑  收藏  举报

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