VIJOS P1234 口袋的天空 Accepted

思路很简单，用kruskal算法生成最小生成森林。kruskal用并查集实现。用堆优化一下才能过。

 

#include<stdio.h>

//disjointset
int rank[1001],set[1001];

void Makeset(int x)
...{
        set[x]=x;
        rank[x]=0;
}
int Find(int x)
...{
        if(set[x]!=x)
                set[x]=Find(set[x]);
        return set[x];
}
void Link(int x,int y)
...{
        if(rank[x]>rank[y])
                set[y]=x;
        else...{
                set[x]=y;
                if(rank[x]==rank[y]) rank[y]++;
        }
}
void Union(int x,int y)
...{
        Link(Find(x),Find(y));
}
//disjointset end
typedef struct e
...{
        int a,b,w;
}Edge;
Edge E[10001];

//MinHeap
int heapsize;
void heapify(int i)
...{
        int l=i<<1;
        int r=(i<<1) + 1;
        int smallest;
        if(l<heapsize && E[l].w<E[i].w) smallest=l;
        else smallest=i;
        if(r<heapsize && E[r].w<E[smallest].w) smallest=r;
        if(smallest!=i) ...{
                Edge tmp;
                tmp=E[i];
                E[i]=E[smallest];
                E[smallest]=tmp;
                heapify(smallest);
        }
}
void Build(void)
...{
        int i;
        for(i=heapsize>>1;i>0;i--) heapify(i);
}
Edge Extract(void)
...{
        Edge t;
        t=E[1];
        E[1]=E[heapsize];
        heapsize--;
        heapify(1);
        return t;
}
//min heap end

int n,m,k;

int main(void)
...{
        int i;
        long cost=0;
        Edge tmp;
        FILE *fin=stdin;
        fscanf(fin,"%d %d %d ",&n,&m,&k);
        heapsize=m;
        for(i=1;i<=m;i++)
                fscanf(fin,"%d %d %d",&E[i].a,&E[i].b,&E[i].w);
        Build();
        for(i=1;i<=n;i++) Makeset(i);
        for(i=n;i>k && heapsize;)...{
                tmp=Extract();
                if(Find(tmp.a)!=Find(tmp.b))...{
                        Union(tmp.a,tmp.b);
                        cost+=tmp.w;
                        i--;
                }else continue;
        }
        if (i>k) printf("No Answer "); 
        else printf("%d ",cost);
        return 0;
}