POJ 2377

#include<stdio.h>
#define MAXN 1005
#include<iostream>
#include<algorithm>
#define inf 10000000
using namespace std;
int _m[MAXN][MAXN];
int low_cost[MAXN];
int pre[MAXN];
unsigned prime(int n);
int DFS(int i,int sum,int p);
bool mark[MAXN];
int main()
{
    //freopen("acm.acm","r",stdin);
    int p;
    int edge;
    unsigned tem;
    int i;
    int j;
    int u;
    int v;
    while(cin>>p>>edge)
    {
        memset(mark,false,sizeof(mark));
        for(i = 0; i < p; ++ i)
        {
            for(j = 0; j < p; ++ j)
                _m[i][j] = inf;
        }
        for(i = 0; i < edge; ++ i)
        {
            cin>>u>>v;
            -- u;
            -- v;
            cin>>tem;
            if(_m[u][v] == inf)
            {
                _m[u][v] = tem;
                _m[u][v] *= -1;
                _m[v][u] = _m[u][v];
            }
            else
                if(tem > _m[u][v]*(-1))
                {
                    _m[u][v] = tem;            
                    _m[u][v] *= -1;
                    _m[v][u] = _m[u][v];
                }
        }
        mark[0] = true;
        tem = -prime(p);
        if(DFS(0,1,p) == p)
            cout<<tem<<endl;
        else
            cout<<-1<<endl;
    }
}
int DFS(int i,int sum,int n)
{
    int j;
    for(j = 0; j < n; ++ j)
    {
        if(i != j && _m[i][j] != inf && !mark[j])
        {
            mark[j] = true;
            sum = DFS(j,sum+1,n);
        }
    }
    return sum;
}
unsigned prime(int n)
{
    int i;
    int j;
    int k;
    unsigned sum = 0;
    int min;
    for(i = 1; i < n; ++ i)
    {
        low_cost[i] = _m[0][i];
        pre[i] = 0;
    }
    for(i = 1; i < n; ++ i)
    {
        min = inf;
        for(j = 1; j < n; ++ j)
        {
            if(low_cost[j]&&low_cost[j] < min)
            {
                k = j;
                min = low_cost[j];
            }
        }
        sum += low_cost[k];
        low_cost[k] = 0;
        for(j = 1; j < n; ++ j)
        {
            if(_m[k][j] < low_cost[j] && low_cost[j])
            {
                low_cost[j] = _m[k][j];
                pre[j] = k;
            }
        }
    }
    return sum;
}