【POJ 2485】Highways（Prim最小生成树）

#include <cstdio>
#define max(x, y) ((x) > (y) ? (x) : (y))
#define N 505
int t, n, g[N][N], lowcost[N], used[N], ans;
void prim(){
    for(int i = 1; i <= n; i++){
        lowcost[i] = g[1][i];
        used[i] = 0;
    }
    used[1] = 1;
    ans = 0;
    for(int i = 1; i <= n; i++){
        int j=1;
        while(used[j]) j++;
        for(int k = 1; k <= n; k++)
            if(!used[k] && lowcost[k] < lowcost[j])
                j = k;
        ans = max(ans, lowcost[j]);
        used[j] = 1;
        for(int k = 1; k <= n; k++)
            if(!used[k] && g[j][k] < lowcost[k])
                lowcost[k] = g[j][k];
    }
}
int main(){
    scanf("%d", &t);
    while(t--){
        scanf("%d", &n);
        for(int i = 1; i <= n; i++)
            for(int j = 1; j <= n; j++)
                scanf("%d", &g[i][j]);
        prim();
        printf("%d\n", ans);
    }
    return 0;
}