最大流增广路(KM算法) HDOJ 1533 Going Home

题目传送门

 /*
     最小费用流：KM算法是求最大流，只要w = -w就可以了，很经典的方法
 */
 #include <cstdio>
 #include <cmath>
 #include <algorithm>
 #include <cstring>
 using namespace std;

 const int MAXN = 1e2 + ;
 const int INF = 0x3f3f3f3f;
 int x[MAXN], y[MAXN];
 int w[MAXN][MAXN];
 int visx[MAXN], visy[MAXN];
 int ly[MAXN];
 int mx[MAXN], my[MAXN];
 int hx[MAXN], hy[MAXN];
 char maze[MAXN][MAXN];
 int n, m, un, vn, d;

 bool DFS(int u) {
     visx[u] = true;
     for (int i=; i<=un; ++i)   {
         if (!visy[i] && x[u] + y[i] == w[u][i]) {
             visy[i] = true;
             if (ly[i] == - || DFS (ly[i])) {
                 ly[i] = u;  return true;
             }
         }
         else if (x[u] + y[i] > w[u][i]) d = min (d, x[u] + y[i] - w[u][i]);
     }
     return false;
 }

 int KM(void)    {
     for (int i=; i<=un; ++i)   {
         x[i] = -INF;
         for (int j=; j<=vn; ++j)   {
             x[i] = max (x[i], w[i][j]);
         }
     }

     memset (ly, -, sizeof (ly));
     memset (y, , sizeof (y));
     for (int i=; i<=un; ++i)    {
         while (true)    {
             memset (visx, false, sizeof (visx));
             memset (visy, false, sizeof (visy));
             d = INF;
             if (DFS (i))    break;
             for (int i=; i<=un; ++i)   {
                 if (visx[i])    x[i] -= d;
             }
             for (int j=; j<=vn; ++j)   {
                 if (visy[j])    y[j] += d;
             }
         }
     }

     int res = ;
     for (int i=; i<=un; ++i)   {
         res += x[i] + y[i];
     }

     return res;
 }

 int main(void)  {       //HDOJ 1533 Going Home
     //freopen ("HDOJ_1533.in", "r", stdin);

     while (scanf ("%d%d", &n, &m) == ) {
         if (!n && !m)   break;
         for (int i=; i<=n; ++i)    {
             scanf ("%s", maze[i] + );
         }
         un = vn = ;
         for (int i=; i<=n; ++i)    {
             for (int j=; j<=m; ++j)    {
                 if (maze[i][j] == 'm')  mx[++un] = i, my[un] = j;
                 else if (maze[i][j] == 'H') hx[++vn] = i, hy[vn] = j;
             }
         }
         for (int i=; i<=un; ++i)   {
             for (int j=; j<=vn; ++j)   {
                 w[i][j] = -(abs (mx[i] - hx[j]) + abs (my[i] - hy[j]));
             }
         }
         printf ("%d\n", -KM ());
     }

     return ;
 }