【HDU2122】Ice_cream’s world III（MST基础题）

2坑，3次WA。

1.判断重边取小。2.自边舍去。

（个人因为vis数组忘记初始化，WA了3次，晕死！！）

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <cctype>
#include <algorithm>
#include <numeric>

#define typec int
using namespace std;

const int V = 1005;
const typec inf = 0xffff;
int vis[V];
typec lowc[V];
int Map[V][V];

typec prim (typec cost[][V], int n) {
    int i, j, p;
    typec minc, res = 0;
    memset(vis, 0, sizeof(vis));
    vis[0] = 1;
    for (i = 1; i < n; ++ i) lowc[i] = cost[0][i];
    for (i = 1; i < n; ++ i) {
        minc = inf; p = -1;
        for (j = 0 ; j < n; ++ j) {
            if (0 == vis[j] && minc > lowc[j]) {
                minc = lowc[j]; p = j;
            }
        }
        if (inf == minc) return -1;
        res += minc; vis[p] = 1;
        for (j = 0 ; j < n; ++ j) {
            if (0 == vis[j] && lowc[j] > cost[p][j]) {
                lowc[j] = cost[p][j];
            }
        }
    }
    return res;
}

int main () {
    int n, road_n;
    int cur = 0;
    while (cin >> n >> road_n) {
        /*if (cur ++ != 0) {
            cout << endl;
        }*/
        for (int i = 0 ; i < n; ++ i) {
            for (int j = 0 ; j < n; ++ j) {
                if (i == j) Map[i][j] = 0;
                else {
                    Map[i][j] = inf;
                }
            }
        }

        for (int i = 0 ; i < road_n; ++ i) {
            int x, y, c;
            scanf("%d%d%d", &x, &y, &c);
            if (x == y) {
                continue;
            }
            Map[x][y] = Map[y][x] = min(Map[x][y], c);
        }

        int ans = prim (Map, n);

        if (ans == -1) {
            cout << "impossible" << endl << endl;
        } else {
            cout << ans << endl << endl;
        }
    }
    return 0;
}