POJ-3026 Borg Maze---BFS预处理+最小生成树

  1 #include<iostream>
  2 #include<cstdio>
  3 #include<cstring>
  4 #include<algorithm>
  5 #include<cmath>
  6 #include<queue>
  7 #include<stack>
  8 #include<map>
  9 #include<sstream>
 10 using namespace std;
 11 typedef long long ll;
 12 typedef pair<int, int> Pair;
 13 const int maxn = 1e2 + 10;
 14 const int INF = 0x3f3f3f3f;
 15 int dir[4][2] = {1,0,0,1,-1,0,0,-1};
 16 int T, n, m, x;
 17 int Map[maxn][maxn];//存图
 18 int lowcost[maxn], mst[maxn];
 19 void prim(int u, int n)//最小生成树起点
 20 {
 21     int sum_mst = 0;//最小生成树权值
 22     for(int i = 0; i < n; i++)//初始化两个数组
 23     {
 24         lowcost[i] = Map[u][i];
 25         mst[i] = u;
 26     }
 27     mst[u] = -1;//设置成-1表示已经加入mst
 28     for(int i = 0; i < n; i++)
 29     {
 30         int minn = INF;
 31         int v = -1;
 32         //在lowcost数组中寻找未加入mst的最小值
 33         for(int j = 0; j < n; j++)
 34         {
 35             if(mst[j] != -1 && lowcost[j] < minn)
 36             {
 37                 v = j;
 38                 minn = lowcost[j];
 39             }
 40         }
 41         if(v != -1)//v=-1表示未找到最小的边,
 42         {//v表示当前距离mst最短的点
 43             //printf("%d %d %d\n", mst[v], v, lowcost[v]);//输出路径
 44             mst[v] = -1;
 45             sum_mst += lowcost[v];
 46             for(int j = 0; j < n; j++)//更新最短边
 47             {
 48                 if(mst[j] != -1 && lowcost[j] > Map[v][j])
 49                 {
 50                     lowcost[j] = Map[v][j];
 51                     mst[j] = v;
 52                 }
 53             }
 54         }
 55     }
 56     //printf("weight of mst is %d\n", sum_mst);
 57     cout<<sum_mst<<endl;
 58 }
 59 string s[55];
 60 vector<Pair>a;
 61 int vis[55][55];
 62 void bfs(int u, int x, int y)//BFS预处理，将x，y为起点进行遍历，求出每个点离当前点距离，更新出Map距离出来
 63 {
 64     queue<Pair>q;
 65     q.push(Pair(x, y));
 66 
 67     memset(vis, -1, sizeof(vis));
 68     vis[x][y] = 0;
 69     while(!q.empty())
 70     {
 71         Pair now = q.front();
 72         q.pop();
 73         for(int i = 0; i < 4; i++)
 74         {
 75             int xx = now.first + dir[i][0];
 76             int yy = now.second + dir[i][1];
 77             if(xx >= 0 && xx < n && yy >= 0 && yy < m && s[xx][yy] != ‘#‘ && vis[xx][yy] == -1)
 78             {
 79                 vis[xx][yy] = vis[now.first][now.second] + 1;
 80                 q.push(Pair(xx, yy));
 81             }
 82         }
 83     }/*
 84     for(int i = 0; i < n; i++)
 85     {
 86         for(int j = 0; j < m; j++)cout<<vis[i][j]<<" ";
 87         cout<<endl;
 88     }*/
 89     for(int i = 0; i < a.size(); i++)
 90     {
 91         if(i == u)continue;
 92         Map[u][i] = vis[a[i].first][a[i].second];
 93     }
 94 }
 95 int main()
 96 {
 97     cin >> T;
 98     getchar();
 99     while(T--)
100     {
101         for(int i = 0; i < 55; i++)s[i].clear();
102         char cc[5];
103         cin >> m >> n;
104         gets(cc);
105         a.clear();
106         for(int i = 0; i < n; i++)
107         {
108             getline(cin, s[i]);
109             for(int j = 0; j < m; j++)
110                 if(s[i][j] == ‘S‘ || s[i][j] == ‘A‘)
111                 a.push_back(Pair(i, j));
112         }
113         for(int i = 0; i < a.size(); i++)
114         {
115             for(int j = 0; j < a.size(); j++)
116             {
117                 if(i == j)Map[i][j] = 0;
118                 else Map[i][j] = INF;
119             }
120         }
121         for(int i = 0; i < a.size(); i++)
122             bfs(i, a[i].first, a[i].second);
123         /*for(int i = 0; i < a.size(); i++)
124         {
125             for(int j = 0; j < a.size(); j++)
126             {
127                 cout<<Map[i][j]<<" ";
128             }
129             cout<<endl;
130         }*/
131         prim(0, a.size());
132     }
133     return 0;
134 }