UVA 10034 Freckles 最小生成树

虽然是道普通的最小生成树题目，可还是中间出了不少问题，暴露的一个问题是不够细心，不够熟练。所以这篇博客就当记录一下bug吧。

代码一：kruskal

  1 #include<stdio.h>
  2 #include<math.h>
  3 #include<stdlib.h>
  4 #include<string.h>
  5 #define N 110
  6 
  7 typedef struct
  8 {
  9     double x,y;
 10 } Point;
 11 Point point[N];
 12 
 13 typedef struct
 14 {
 15     int u,v;
 16     double c;
 17 } EDGE;
 18 EDGE edge[N*N/2+10];
 19 int m,tc,n,pre[N];
 20 
 21 double cal(Point a,Point b)
 22 {
 23     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
 24 }
 25 int dblcmp(double x)
 26 {
 27     if(fabs(x)<1e-9)
 28         return 0;
 29     return x>0?1:-1;
 30 
 31 }
 32 int cmp(const void*i,const void*j)
 33 {
 34     EDGE *a=(EDGE*)i;
 35     EDGE *b=(EDGE*)j;
 36 
 37     return dblcmp(a->c-b->c);
 38 
 39 }
 40 void add_edge(int u,int v,double c)
 41 {
 42     edge[m].u=u;
 43     edge[m].v=v;
 44     edge[m].c=c;
 45     m++;/*记得更新*/
 46 }
 47 
 48 int find(int u)
 49 {
 50     int x=u;
 51     for(; pre[x]>=0; x=pre[x])  ;/*条件判断应该是是pre[x]>=0*/
 52     while(x!=u)
 53     {
 54         int t=pre[u];
 55         pre[u]=x;
 56         u=t;
 57     }
 58     return x;
 59 }
 60 
 61 double kruskal(void)
 62 {
 63     double ans=0.0;
 64     int num=0;
 65     memset(pre,-1,sizeof(pre));
 66     int i;
 67     qsort(edge,m,sizeof(EDGE),cmp);/*sort before algorithm*/
 68     /*for(i=0;i<m;i++)
 69         printf("%f\n",edge[i].c);  */
 70     for(i=0; i<m; i++)
 71     {
 72         int u=edge[i].u;
 73         int v=edge[i].v;
 74         int x,y;
 75         if((x=find(u))!=(y=find(v)))
 76         {
 77             ans=ans+edge[i].c;
 78             pre[x]=y;
 79             num++;
 80         }
 81         if(num==n-1)
 82             break;
 83     }
 84     return ans;
 85 }
 86 
 87 
 88 void input(void)
 89 {
 90     m=0;
 91     scanf("%d",&n);
 92     int i,j;
 93     for(i=0; i<n; i++)
 94         scanf("%lf%lf",&point[i].x,&point[i].y);
 95 
 96     for(i=0; i<n-1; i++)
 97         for(j=i+1; j<n; j++)
 98         {
 99             double s=cal(point[i],point[j]);
100             add_edge(i,j,s);
101         }
102 
103 }
104 
105 void solve()
106 {
107     double mst;
108     mst=kruskal();
109     printf("%.2f\n",mst);
110     if(tc)
111         puts("");
112 }
113 
114 int main(void)
115 {
116     scanf("%d",&tc);
117     while(tc--)
118     {
119         input();
120         solve();
121     }
122     return 0;
123 }

代码二：prim

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cmath>
 4 #include<cstring>
 5 #define N 110
 6 #define INF 1000000000000000/*这里要开大于点，不然WA*/
 7 
 8 using namespace std;
 9 int n,tc;
10 double dis[N][N];
11 double x[N],y[N];
12 
13 double cal(double x1,double y1,double x2,double y2)
14 {
15     return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
16 }
17 
18 void input(void)
19 {
20     scanf("%d",&n);
21     int i,j;
22     for(i=0; i<n; i++)
23         scanf("%lf%lf",x+i,y+i);
24     for(i=0; i<n-1; i++)
25         for(j=i+1; j<n; j++)
26             dis[i][j]=dis[j][i]=cal(x[i],y[i],x[j],y[j]);
27 }
28 
29 double Prim(void)
30 {
31     double lowcost[N];
32     int vis[N];
33     memset(vis,0,sizeof(vis));
34     for(int i=0; i<N; i++)
35         lowcost[i]=INF;
36     vis[0]=-1;
37     int e=0,i;
38     double ans=0;
39     for(int k=0; k<n-1; k++)
40     {
41         double micost=INF;
42         int miedge=-1;
43         for( i=0; i<n; i++)
44             if(vis[i]!=-1)
45             {
46                 double temp=dis[e][i];
47                 if(temp<lowcost[i])
48                 {
49                     lowcost[i]=temp;
50                     vis[i]=e;
51                 }
52                 if(lowcost[i]<micost)
53                     micost=lowcost[miedge=i];
54             }
55         ans+=micost;
56         e=miedge;/*表示miedge这个顶点作为加入点*/
57         vis[miedge]=-1;/*用来记录下次加入的点*/
58     }
59     return ans;
60 }
61 
62 void solve(void)
63 {
64     double mst=Prim();
65     printf("%.2f\n",mst);
66     if(tc)
67         puts("");
68 }
69 
70 int main()
71 {
72     scanf("%d",&tc);
73     while(tc--)
74     {
75         input();
76         solve();
77     }
78     return 0;
79 }