HDU 1863 畅通工程

读入边权要注意是否比原来的边权小

#include <iostream>
#include <fstream>
#include <string.h>
using namespace std;
const int MAXN = 1000;
int G[MAXN][MAXN];
int lowcost[MAXN];
int cloest[MAXN];
bool used[MAXN];
int cost;

void PRIM(int n){
    int cnt = 0;
    cost = 0;
    used[1] = true;
    for(int i = 2; i <= n; i++){
        lowcost[i] = G[i][1];
        cloest[i] = 1;
        used[i] = false;
    }
    for(int i = 1; i < n; i++){
        int min = 32767, minIndex = i;
        for(int j = 1; j <= n; j++){
            if( !used[j] && lowcost[j] < min){
                min = lowcost[j];
                minIndex = j;
            }
        }
        if(min == 32767){
            break;
        }
        cost += min;
        used[minIndex] = true;
        cnt++;
        for(int j = 1; j <= n; j++){
            if( !used[j] && lowcost[j] > G[minIndex][j]){
                lowcost[j] = G[minIndex][j];
                cloest[j] = minIndex;
            }
        }
    }
    if( cnt != n - 1)
        cout << "?" << endl;
    else
        cout << cost << endl;
}

int main(){
    int n, m, x, y, weight;
    while(cin >> n >> m){
        if( n == 0)
            break;
        //memset(G,32767,sizeof(G));
        for(int i = 0; i < 1000; ++i)
            for(int j = 0; j < 1000; ++j){
                G[i][j] = 32767;
            }
        for(int i = 1; i <= n;i++){
            cin >> x >> y >> weight;
            G[x][y] = G[x][y] < weight ? G[x][y]:weight;    //陷阱
            G[y][x] = G[x][y];
            //G[x][y] = G[x][y] < weight ? G[x][y]:weight;
            //G[y][x] = G[x][y] = weight;
        }
        //cout << cost << endl;
        if( n < m - 1)
            cout << "?" << endl;
        else
            PRIM(m);
    }
    return 0;
}