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

 #include<stdio.h>
 #include<math.h>
 #include<stdlib.h>
 #include<string.h>
 #define N 110

 typedef struct
 {
     double x,y;
 } Point;
 Point point[N];

 typedef struct
 {
     int u,v;
     double c;
 } EDGE;
 EDGE edge[N*N/+];
 int m,tc,n,pre[N];

 double cal(Point a,Point b)
 {
     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
 }
 int dblcmp(double x)
 {
     if(fabs(x)<1e-)
         return ;
     return x>?:-;

 }
 int cmp(const void*i,const void*j)
 {
     EDGE *a=(EDGE*)i;
     EDGE *b=(EDGE*)j;

     return dblcmp(a->c-b->c);

 }
 void add_edge(int u,int v,double c)
 {
     edge[m].u=u;
     edge[m].v=v;
     edge[m].c=c;
     m++;/*记得更新*/
 }

 int find(int u)
 {
     int x=u;
     for(; pre[x]>=; x=pre[x])  ;/*条件判断应该是是pre[x]>=0*/
     while(x!=u)
     {
         int t=pre[u];
         pre[u]=x;
         u=t;
     }
     return x;
 }

 double kruskal(void)
 {
     double ans=0.0;
     int num=;
     memset(pre,-,sizeof(pre));
     int i;
     qsort(edge,m,sizeof(EDGE),cmp);/*sort before algorithm*/
     /*for(i=0;i<m;i++)
         printf("%f\n",edge[i].c);  */
     for(i=; i<m; i++)
     {
         int u=edge[i].u;
         int v=edge[i].v;
         int x,y;
         if((x=find(u))!=(y=find(v)))
         {
             ans=ans+edge[i].c;
             pre[x]=y;
             num++;
         }
         if(num==n-)
             break;
     }
     return ans;
 }

 void input(void)
 {
     m=;
     scanf("%d",&n);
     int i,j;
     for(i=; i<n; i++)
         scanf("%lf%lf",&point[i].x,&point[i].y);

     for(i=; i<n-; i++)
         for(j=i+; j<n; j++)
         {
             double s=cal(point[i],point[j]);
             add_edge(i,j,s);
         }

 }

 void solve()
 {
     double mst;
     mst=kruskal();
     printf("%.2f\n",mst);
     if(tc)
         puts("");
 }

 int main(void)
 {
     scanf("%d",&tc);
     while(tc--)
     {
         input();
         solve();
     }
     return ;
 }

代码二：prim

 #include<cstdio>
 #include<iostream>
 #include<cmath>
 #include<cstring>
 #define N 110
 #define INF 1000000000000000/*这里要开大于点，不然WA*/

 using namespace std;
 int n,tc;
 double dis[N][N];
 double x[N],y[N];

 double cal(double x1,double y1,double x2,double y2)
 {
     return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
 }

 void input(void)
 {
     scanf("%d",&n);
     int i,j;
     for(i=; i<n; i++)
         scanf("%lf%lf",x+i,y+i);
     for(i=; i<n-; i++)
         for(j=i+; j<n; j++)
             dis[i][j]=dis[j][i]=cal(x[i],y[i],x[j],y[j]);
 }

 double Prim(void)
 {
     double lowcost[N];
     int vis[N];
     memset(vis,,sizeof(vis));
     for(int i=; i<N; i++)
         lowcost[i]=INF;
     vis[]=-;
     int e=,i;
     double ans=;
     for(int k=; k<n-; k++)
     {
         double micost=INF;
         int miedge=-;
         for( i=; i<n; i++)
             if(vis[i]!=-)
             {
                 double temp=dis[e][i];
                 if(temp<lowcost[i])
                 {
                     lowcost[i]=temp;
                     vis[i]=e;
                 }
                 if(lowcost[i]<micost)
                     micost=lowcost[miedge=i];
             }
         ans+=micost;
         e=miedge;/*表示miedge这个顶点作为加入点*/
         vis[miedge]=-;/*用来记录下次加入的点*/
     }
     return ans;
 }

 void solve(void)
 {
     double mst=Prim();
     printf("%.2f\n",mst);
     if(tc)
         puts("");
 }

 int main()
 {
     scanf("%d",&tc);
     while(tc--)
     {
         input();
         solve();
     }
     return ;
 }