POJ-1258(Agri-Net) Prim

POJ-1258

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int INF = 0x3f3f3f3f;
const int MAXN = 105;
int cost[MAXN][MAXN];
int lowcost[MAXN];
int visit[MAXN];

int prim(int n){
    memset(visit, 0, sizeof(visit));
    for(int i = 1; i <= n; ++i) lowcost[i] = cost[1][i];
    visit[1] = 1;
    lowcost[1] = 0;
    int res = 0;
    for(int i = 2; i <= n; ++i)
    {
        int minc = INF;
        int flag = -1;
        for(int j = 1; j <= n; ++j)
        {
            if(!visit[j] && minc > lowcost[j]){
                minc = lowcost[j];
                flag = j;
            }
        }

        if(flag == -1) return -1;
        res += minc;
        visit[flag] = 1;

        for(int j = 1; j <= n; ++j){
            if(!visit[j] && lowcost[j] > cost[flag][j]){
                lowcost[j] = cost[flag][j];
            }
        }
    }
    return res;
}
int main(){
    int n;
    while(cin >> n)
    {
        for(int i = 1; i <= n; ++i)
            for(int j = 1; j <= n; ++j)cin >> cost[i][j];
        cout << prim(n) << endl;
    }
    return 0;
}