7-50 畅通工程之局部最小花费问题 (35分)--prim

31分代码，还有最后一个测试点没过

#include<iostream>
#include <map>
using namespace std;
#define infinite 100000000
int main()
{
    int built[101][101];
    long long int cost[101][101];//两个村庄之间道路费用
    long long int low[101];//最小生成树到村庄的最短距离
    int N;
    cin >> N;
    for (int i = 1; i <= N; i++)low[i] = infinite;
    for (int i = 1; i <= N; i++)
        for (int j = 1; j <= N; j++)
            cost[i][j] = cost[j][i] = infinite;
    for (int i = 0; i < N * (N - 1) / 2; i++)
    {
        int a, b;
        cin >> a >> b;
        cin >> cost[a][b];
        cost[b][a] = cost[a][b];
        cin >> built[a][b];
        built[b][a] = built[a][b];
        if (built[a][b] == 1)
        {
            low[a] = low[b] = 0;
            for (int i = 1; i <= N; i++)
            {
                if (cost[a][i] < low[i])
                    low[i] = cost[a][i];
                if (cost[b][i] < low[i])
                    low[i] = cost[b][i];
            }
        }
    }
    low[1] = 0;
    for (int i = 1; i <= N; i++)
    {
        if(cost[1][i] < low[i])
        low[i] = cost[1][i];
    }
  long long int sum = 0;
  for (int c = 0; c < N-1; c++)//prim算法
  {
    int min = infinite;
    int k = -1;
    for (int i = 1; i <= N; i++)
    {
      if (low[i] < min && low[i] != 0)
      {
        min = low[i];
        k = i;
      }
    }
    if (k == -1)break;
    sum += min;
    low[k] = 0;
    for (int x = 1; x <= N; x++)
    {
      if (cost[k][x] < low[x] && low[x] != 0)
      {
        low[x] = cost[k][x];
      }
    }
  }
  cout << sum;
  return 0;
}