剪枝还是挺多的，不过都比较容易想，主要是复习一下奇偶性剪枝。
1 #include <iostream> 2 #include <cstring> 3 #include <cstdio> 4 #include <cmath> 5 using namespace std; 6 7 const int N = 7; 8 char maze[N][N]; 9 int dx[] = { 0, 0, 1, -1 }; 10 int dy[] = { 1, -1, 0, 0 }; 11 int sx, sy, ex, ey; 12 int n, m, t, wall; 13 14 bool ok( int x, int y ) 15 { 16 return x >= 0 && x < n && y >= 0 && y < m && maze[x][y] == '.'; 17 } 18 19 bool dfs( int x, int y, int step ) 20 { 21 if ( step == t ) 22 { 23 if ( x == ex && y == ey ) return true; 24 return false; 25 } 26 int d1 = abs( ex - x ) + abs( ey - y ); 27 int d2 = abs( t - step ); 28 if ( d2 < d1 ) return false; 29 for ( int i = 0; i < 4; i++ ) 30 { 31 int xx = x + dx[i]; 32 int yy = y + dy[i]; 33 if ( ok( xx, yy ) ) 34 { 35 maze[xx][yy] = 'X'; 36 if ( dfs( xx, yy, step + 1 ) ) return true; 37 maze[xx][yy] = '.'; 38 } 39 } 40 return false; 41 } 42 43 int main () 44 { 45 while ( scanf("%d%d%d", &n, &m, &t) != EOF ) 46 { 47 if ( !n && !m && !t ) break; 48 wall = 0; 49 for ( int i = 0; i < n; i++ ) 50 { 51 scanf("%s", maze[i]); 52 for ( int j = 0; j < m; j++ ) 53 { 54 if ( maze[i][j] == 'S' ) 55 { 56 sx = i; 57 sy = j; 58 maze[i][j] = 'X'; 59 wall++; 60 } 61 else if ( maze[i][j] == 'D' ) 62 { 63 ex = i; 64 ey = j; 65 maze[i][j] = '.'; 66 } 67 else if ( maze[i][j] == 'X' ) 68 { 69 wall++; 70 } 71 } 72 } 73 int d = abs( ex - sx ) + abs( ey - sy ); 74 if ( ( d & 1 ) == ( t & 1 ) && n * m - wall >= t ) 75 { 76 if ( dfs( sx, sy, 0 ) ) 77 { 78 puts("YES"); 79 } 80 else 81 { 82 puts("NO"); 83 } 84 } 85 else 86 { 87 puts("NO"); 88 } 89 } 90 return 0; 91 }