NYOJ 78 圈水池

http://acm。nyist。net/JudgeOnline/problem。php?pid=78

原来Graham都是模板直接上的,这次是自己写的,发现自己尽是细节没搞好

View Code
 1 #include <iostream>
 2 #include <algorithm>
 3 using namespace std;
 4 const int maxn = 105;
 5 struct Point
 6 {
 7     float x,y;
 8 }p[maxn],stack[maxn];
 9 
10 double xmult(Point p1,Point p2,Point p0)        //cross product 
11 {
12     return (p1.x-p0.x)*(p2.y-p0.y)-(p1.y-p0.y)*(p2.x-p0.x);
13 }
14 
15 double dis(Point p1,Point p2)        //distance
16 {
17     return (p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y);
18 }
19 
20 bool cmp(Point a,Point b)    //sort the element of the point besides p[0]
21 {
22     double has;
23     has=xmult(a,b,p[0]);
24     if(has>0)        // a is the right of the b
25         return 1;
26     else if((has==0)&& (dis(a,p[0])<dis(b,p[0])))        //sort by distance
27         return 1;
28     else
29         return 0;        //a is the left of th b
30 }
31 
32 void swap(int r,int s)      
33 {
34     Point temp;
35     temp=p[r];
36     p[r]=p[s];
37     p[s]=temp;
38 }
39 
40 //Graham
41 int Graham(int n)
42 {
43     int i,top,k;
44     Point ans;
45     top=2;
46     if(n<=3)        
47     {
48         for(i=0;i<n;i++)
49             stack[i]=p[i];
50         return n;
51     }
52     k=0;
53     for(i=1;i<n;i++)        //find the left-under point
54     if((p[i].y<p[k].y )|| ((p[i].y==p[k].y)&&(p[i].x<p[k].x)))
55         k=i;
56     ans=p[0];    p[0]=p[k];    p[k]=ans;        //set the left-under to the p[0]
57     sort(p+1,p+n,cmp);    
58     for(i=0;i<=top;i++)
59         stack[i]=p[i];
60     for(i=top+1;i<n;i++)
61     {
62         if((i+1<n)&&(xmult(p[i],p[i+1],p[0])==0))        //the point in a line
63             continue;
64         while(xmult(p[i],stack[top],stack[top-1])>=0)        //if the p[i] is the right of the stack[top]
65                     top--;                                        //choose the p[i]
66         stack[++top]=p[i];    
67     }
68     return ++top;
69 }
70 
71 bool cmp_xy(Point a,Point b)
72 {
73     if(a.x!=b.x)
74         return a.x<b.x;
75     else
76         return a.y<b.y;
77 }
78 
79 int main()
80 {
81     int i,j,t,n,top;
82     cin>>t;
83     while(t--)
84     {
85         cin>>n;
86         for(i=0;i<n;i++)
87             cin>>p[i].x>>p[i]。y;
88         top=Graham(n);
89         sort(stack,stack+top,cmp_xy);
90         for(i=0;i<top;i++)
91             cout<<stack[i].x<<" "<<stack[i].y<<endl;
92     }
93     return 0;
94 }
 
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