POJ 2195 Going Home

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <queue>
  5 #define pii pair<int,int>
  6 #define INF 0x3f3f3f3f
  7 using namespace std;
  8 const int maxn = 200;
  9 struct arc {
 10     int to,flow,cost,next;
 11     arc(int x = 0,int y = 0,int z = 0,int nxt = -1) {
 12         to = x;
 13         flow = y;
 14         cost = z;
 15         next = nxt;
 16     }
 17 } e[maxn*maxn];
 18 int head[maxn*10],d[maxn*10],p[maxn*10],n,m;
 19 char mp[maxn][maxn];
 20 bool in[maxn*10];
 21 int hs[maxn][maxn],pid,hid,S,T,tot;
 22 void add(int u,int v,int flow,int cost) {
 23     e[tot] = arc(v,flow,cost,head[u]);
 24     head[u] = tot++;
 25     e[tot] = arc(u,0,-cost,head[v]);
 26     head[v] = tot++;
 27 }
 28 bool isIn(int x,int y) {
 29     return x >= 0 && x < n && y >= 0 && y < m;
 30 }
 31 void bfs(int x,int y) {
 32     queue< pii >q;
 33     q.push(make_pair(x,y));
 34     int ds[maxn][maxn];
 35     memset(ds,-1,sizeof(ds));
 36     ds[x][y] = 0;
 37     static const int dir[4][2] = {-1,0,1,0,0,-1,0,1};
 38     while(!q.empty()) {
 39         pii now = q.front();
 40         q.pop();
 41         for(int i = 0; i < 4; ++i) {
 42             int tx = now.first + dir[i][0];
 43             int ty = now.second + dir[i][1];
 44             if(isIn(tx,ty) && ds[tx][ty] == -1) {
 45                 ds[tx][ty] = ds[now.first][now.second] + 1;
 46                 q.push(make_pair(tx,ty));
 47                 if(mp[tx][ty] == ‘H‘)
 48                     add(hs[x][y],pid+hs[tx][ty],1,ds[tx][ty]);
 49             }
 50         }
 51     }
 52 }
 53 bool spfa() {
 54     queue<int>q;
 55     for(int i = 0; i <= T; ++i) {
 56         d[i] = INF;
 57         in[i] = false;
 58         p[i] = -1;
 59     }
 60     d[S] = 0;
 61     q.push(S);
 62     while(!q.empty()) {
 63         int u = q.front();
 64         q.pop();
 65         in[u] = false;
 66         for(int i = head[u]; ~i; i = e[i].next) {
 67             if(e[i].flow && d[e[i].to] > d[u] + e[i].cost) {
 68                 d[e[i].to] = d[u] + e[i].cost;
 69                 p[e[i].to] = i;
 70                 if(!in[e[i].to]) {
 71                     in[e[i].to] = true;
 72                     q.push(e[i].to);
 73                 }
 74             }
 75         }
 76     }
 77     return p[T] > -1;
 78 }
 79 
 80 int solve() {
 81     int ans = 0;
 82     while(spfa()) {
 83         int minF = INF;
 84         for(int i = p[T]; ~i; i = p[e[i^1].to])
 85             minF = min(minF,e[i].flow);
 86         for(int i = p[T]; ~i; i = p[e[i^1].to]) {
 87             e[i].flow -= minF;
 88             e[i^1].flow += minF;
 89         }
 90         ans += d[T]*minF;
 91     }
 92     return ans;
 93 }
 94 int main() {
 95     while(scanf("%d %d",&n,&m),n||m) {
 96         memset(head,-1,sizeof(head));
 97         hid = pid = 0;
 98         for(int i = tot = 0; i < n; ++i) {
 99             scanf("%s",mp[i]);
100             for(int j = 0; j < m; ++j)
101                 if(mp[i][j] == ‘H‘) hs[i][j] = hid++;
102                 else if(mp[i][j] == ‘m‘) hs[i][j] = pid++;
103         }
104         S = hid + pid;
105         T = S + 1;
106         for(int i = 0; i < n; ++i)
107             for(int j = 0; j < m; ++j)
108                 if(mp[i][j] == ‘m‘) {
109                     bfs(i,j);
110                     add(S,hs[i][j],1,0);
111                 } else if(mp[i][j] == ‘H‘) add(hs[i][j]+pid,T,1,0);
112         printf("%d\n",solve());
113     }
114     return 0;
115 }