最大流增广路(KM算法) HDOJ 1533 Going Home

 

题目传送门

 1 /*  2  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  3 */  4 #include <cstdio>  5 #include <cmath>  6 #include <algorithm>  7 #include <cstring>  8 using namespace std;  9 10 const int MAXN = 1e2 + 10; 11 const int INF = 0x3f3f3f3f; 12 int x[MAXN], y[MAXN]; 13 int w[MAXN][MAXN]; 14 int visx[MAXN], visy[MAXN]; 15 int ly[MAXN]; 16 int mx[MAXN], my[MAXN]; 17 int hx[MAXN], hy[MAXN]; 18 char maze[MAXN][MAXN]; 19 int n, m, un, vn, d; 20 21 bool DFS(int u) { 22 visx[u] = true; 23 for (int i=1; i<=un; ++i) { 24 if (!visy[i] && x[u] + y[i] == w[u][i]) { 25 visy[i] = true; 26 if (ly[i] == -1 || DFS (ly[i])) { 27 ly[i] = u; return true; 28  } 29  } 30 else if (x[u] + y[i] > w[u][i]) d = min (d, x[u] + y[i] - w[u][i]); 31  } 32 return false; 33 } 34 35 int KM(void) { 36 for (int i=1; i<=un; ++i) { 37 x[i] = -INF; 38 for (int j=1; j<=vn; ++j) { 39 x[i] = max (x[i], w[i][j]); 40  } 41  } 42 43 memset (ly, -1, sizeof (ly)); 44 memset (y, 0, sizeof (y)); 45 for (int i=1; i<=un; ++i) { 46 while (true) { 47 memset (visx, false, sizeof (visx)); 48 memset (visy, false, sizeof (visy)); 49 d = INF; 50 if (DFS (i)) break; 51 for (int i=1; i<=un; ++i) { 52 if (visx[i]) x[i] -= d; 53  } 54 for (int j=1; j<=vn; ++j) { 55 if (visy[j]) y[j] += d; 56  } 57  } 58  } 59 60 int res = 0; 61 for (int i=1; i<=un; ++i) { 62 res += x[i] + y[i]; 63  } 64 65 return res; 66 } 67 68 int main(void) { //HDOJ 1533 Going Home 69 //freopen ("HDOJ_1533.in", "r", stdin); 70 71 while (scanf ("%d%d", &n, &m) == 2) { 72 if (!n && !m) break; 73 for (int i=1; i<=n; ++i) { 74 scanf ("%s", maze[i] + 1); 75  } 76 un = vn = 0; 77 for (int i=1; i<=n; ++i) { 78 for (int j=1; j<=m; ++j) { 79 if (maze[i][j] == 'm') mx[++un] = i, my[un] = j; 80 else if (maze[i][j] == 'H') hx[++vn] = i, hy[vn] = j; 81  } 82  } 83 for (int i=1; i<=un; ++i) { 84 for (int j=1; j<=vn; ++j) { 85 w[i][j] = -(abs (mx[i] - hx[j]) + abs (my[i] - hy[j])); 86  } 87  } 88 printf ("%d\n", -KM ()); 89  } 90 91 return 0; 92 }