[2016-04-14][POJ][1287][Networking]

• 时间:2016-04-14 14:48:44 星期四

• 题目编号:[2016-04-14][POJ][1287][Networking]

• 题目大意:求最小生成树

• 分析:直接prim算法,更新边的时候,重边取最小值

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn = 50 + 10;
const int inf = 0x3f3f3f3f;
int g[maxn][maxn],vis[maxn],lowc[maxn];
int prim(int n){
        int ans = 0;
        memset(vis,0,sizeof(vis));
        for(int i = 2 ; i <=  n ; ++i)        lowc[i] = g[1][i];
        vis[1] = 1;
        for(int i = 2 ; i <= n ;++i){
                int minc = inf;
                int p = -1;
                for(int j = 1 ;j <= n ;++j){
                        if(!vis[j] && minc > lowc[j]){
                                minc = lowc[j];
                                p = j;
                        }
                }
                if(minc == inf)        return -1;
                ans += minc;
                vis[p] = 1;
                for(int j = 1 ; j <= n ; ++j){
                        if(!vis[j] && lowc[j] > g[p][j])
                                lowc[j] = g[p][j];
                }
        }
        return ans;
}
int main(){
        //freopen("in.txt","r",stdin);
        int n,m;
        while(~scanf("%d",&n) && n){
                scanf("%d",&m);
                int a,b,c;
                memset(g,0x3f,sizeof(g));
                for(int i = 1; i <= m ; ++i ){
                        scanf("%d%d%d",&a,&b,&c);
                        g[a][b] = min(c,g[a][b]);
                        g[b][a] = g[a][b];
                }
                printf("%d\n",prim(n));
        }
        return 0;
}

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