UVA10600 ACM Contest and Blackout

用prim算法求最小生成树和次小生成树~

#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
const int maxn=1014;
const int inf=1e9;
int g[maxn][maxn],d[maxn],visit[maxn],pre[maxn],c[maxn][maxn],N,M;
int path[maxn][maxn];//记录最小生成树里两点之间的路径 
void init () {
    for (int i=0;i<maxn;i++)
    for (int j=0;j<maxn;j++)
    g[i][j]=inf,c[i][j]=0,path[i][j]=0;
} 
int prim (int s) {
    fill (d,d+maxn,inf);
    fill (visit,visit+maxn,0);
    for (int i=1;i<=N;i++) pre[i]=i;
    d[s]=0;
    int ans=0;
    for (int i=1;i<=N;i++) {
        int u=-1,min=inf;
        for (int j=1;j<=N;j++)
        if (visit[j]==false&&d[j]<min) {
            u=j;
            min=d[j];
        } 
        if (u==-1) return -1;
        visit[u]=1;
        ans+=d[u];
        if (pre[u]!=u) c[u][pre[u]]=c[pre[u]][u]=1;
        for (int v=1;v<=N;v++) {
            if (!visit[v]&&g[u][v]!=inf&&g[u][v]<d[v]) d[v]=g[u][v],pre[v]=u;
            if (visit[v]&&v!=u) path[u][v]=path[v][u]=max(path[pre[u]][v],d[u]);
        }
    }
    return ans;
}
int main () {
    int T;
    scanf ("%d",&T);
    while (T--) {
        scanf ("%d %d",&N,&M);
        int x,y;
        init ();
        for (int i=0;i<M;i++) {
            scanf ("%d %d",&x,&y);
            scanf ("%d",&g[x][y]);
            g[y][x]=g[x][y];
        }
        int mst=prim (1);
        int ans=inf;
        for (int i=1;i<=N;i++)
        for (int j=1;j<=N;j++) {
            if (i!=j&&!c[i][j]) {
                ans=min(ans,mst-path[i][j]+g[i][j]);
            } 
        }
        printf ("%d %d\n",mst,ans);
    }
    return 0;
}