POJ 2485

#include<iostream>
#define MAXN 505
#define inf 1000000000
using namespace std;
typedef int elem_t;
int _m[MAXN][MAXN];
int pre[MAXN];
elem_t prim(int n,elem_t mat[][MAXN],int* pre);
int main()
{
    //freopen("acm.acm","r",stdin);
    int num;
    int i;
    int j;
    int min = inf; 
    int time;
    scanf("%d",&time);
    while(time --)
    {
        scanf("%d",&num);
        min = 0; 
        for(i = 0; i < num; ++ i)
        {
            for(j = 0; j < num; ++ j)
                _m[i][j] = inf;
        }
        for(i = 0; i < num; ++ i)
        {
            for(j = 0; j < num; ++ j)
            {
                scanf("%d",&_m[i][j]);
            }
        }
        prim(num,_m,pre);
        for(i  = num-1; i >= 0; -- i)
        {
            j = i;
            while(pre[j] != -1)
            {
                if(_m[pre[j]][j] > min)
                    min = _m[pre[j]][j];
                j = pre[j];
            }
        }
        cout<<min<<endl;
    }
}



////////////////////////////////////////////////

elem_t prim(int n,elem_t mat[][MAXN],int* pre){
    elem_t min[MAXN],ret=0;
    int v[MAXN],i,j,k;
    for (i=0;i<n;i++)
        min[i]=inf,v[i]=0,pre[i]=-1;
    for (min[j=0]=0;j<n;j++){
        for (k=-1,i=0;i<n;i++)
            if (!v[i]&&(k==-1||min[i]<min[k]))
                k=i;
        for (v[k]=1,ret+=min[k],i=0;i<n;i++)
            if (!v[i]&&mat[k][i]<min[i])
                min[i]=mat[pre[i]=k][i];
    }
    return ret;
}