bfs是一层层的遍历下去，每多一层即为多走一步，因此只要遇到T就停，此时肯定是最小步数。
所以这两层bfs应为，先对箱子的最少步数进行bfs，从而求出推箱子所用最少步数；
然后箱子bfs内部嵌入人的bfs，从而箱子每走一步，判断一下这个移动能否由人来完成（由箱子的移动倒推人应该在的位置，看这个位置是否合理）。
一、http://tech.artyoo.me/?p=282
1 #include <map>
2 #include <set>
3 #include <queue>
4 #include <stack>
5 #include <math.h>
6 #include <time.h>
7 #include <stdio.h>
8 #include <stdlib.h>
9 #include <iostream>
10 #include <limits.h>
11 #include <string.h>
12 #include <string>
13 #include <algorithm>
14 #include <iomanip>
15 #define read freopen("in.txt","r",stdin)
16 #define write freopen("out.txt","w",stdout)
17 using namespace std;
18 #define MAXSIZE 22
19 typedef struct {
20 int bx, by, px, py;
21 string path;
22 } Node;
23 typedef struct {
24 int x, y;
25 string path;
26 } Point;
27 int row, col;
28 char grid[MAXSIZE][MAXSIZE];
29 bool vis[MAXSIZE][MAXSIZE][4], vis2[MAXSIZE][MAXSIZE];
30 Node st;
31 int caseID;
32 queue<Node> qb;
33 queue<Point> qp;
34
35 const int dx[] = {-1, 1, 0, 0};
36 const int dy[] = {0, 0, -1, 1};
37 const char Dir[] = {‘N‘, ‘S‘, ‘W‘, ‘E‘};
38 const char dir[] = {‘n‘, ‘s‘, ‘w‘, ‘e‘};
39 string person_path;
40
41 int Min(int a,int b){return a<b?a:b;}
42 int Max(int a,int b){return a>b?a:b;}
43
44 bool bfs_person(Point sp, Point ep, int bx, int by) {
45 person_path = "";
46 memset(vis2, false, sizeof(vis2));
47 while(!qp.empty()) qp.pop();
48 sp.path = "";
49 qp.push(sp);
50 vis2[sp.x][sp.y] = true;
51 while(!qp.empty()) {
52 Point now = qp.front(); qp.pop();
53 if(now.x == ep.x && now.y == ep.y) {
54 person_path = now.path;
55 return true;
56 }
57 for(int d = 0; d < 4; d++) {
58 int x = now.x + dx[d];
59 int y = now.y + dy[d];
60 if(x >= 0 && x < row && y >= 0 && y < col && grid[x][y] != ‘#‘ && !(x == bx && y == by)) {
61 if(!vis2[x][y]) {
62 Point next;
63 next.x = x;
64 next.y = y;
65 next.path = now.path + dir[d];
66 qp.push(next);
67 vis2[x][y] = true;
68 }
69 }
70 }
71 }
72 return false;
73 }
74
75 string bfs_box() {
76 memset(vis, false, sizeof(vis));
77 while(!qb.empty()) qb.pop();
78 qb.push(st);
79 while(!qb.empty()) {
80 Node now;
81 now = qb.front(); qb.pop();
82 if(grid[now.bx][now.by] == ‘T‘) {
83 return now.path;
84 }
85 for(int d = 0; d < 4; d++) {
86 int x = now.bx + dx[d];
87 int y = now.by + dy[d];
88 if(x >= 0 && x < row && y >= 0 && y < col && grid[x][y] != ‘#‘) {
89 if(!vis[x][y][d]) {
90 Point sp, ep; /* sp: 人的当前位置；ep：人要按当前方向推箱子的话必须得到达的位置 */
91 sp.x = now.px; sp.y = now.py;
92 ep.x = now.bx; ep.y = now.by;
93 switch(d) {
94 case 0: ep.x += 1; break;
95 case 1: ep.x -= 1; break;
96 case 2: ep.y += 1; break;
97 case 3: ep.y -= 1; break;
98 }
99 if(ep.x >= 0 && ep.x < row && ep.y >= 0 && ep.y < col && grid[ep.x][ep.y] != ‘#‘) {
100 if(bfs_person(sp, ep, now.bx, now.by)) {
101 Node next;
102 next.bx = x; next.by = y;
103 next.px = now.bx; next.py = now.by;
104 next.path = now.path + person_path + Dir[d];
105 qb.push(next);
106 vis[x][y][d] = true;
107 }
108 }
109 }
110 }
111 }
112 }
113 return "Impossible.";
114 }
115
116 int main() {
117 read; write;
118 caseID = 0;
119 while(scanf("%d%d", &row, &col) && row && col) {
120 getchar();
121 for(int i = 0; i < row; i++) {
122 gets(grid[i]);
123 }
124 for(int i = 0; i < row; i++) {
125 for(int j = 0; j < col; j++) {
126 if(grid[i][j] == ‘B‘) {
127 st.bx = i;
128 st.by = j;
129 grid[i][j] = ‘.‘;
130 } else if(grid[i][j] == ‘S‘) {
131 st.px = i;
132 st.py = j;
133 grid[i][j] = ‘.‘;
134 }
135 }
136 }
137 st.path = "";
138 printf("Maze #%d\n", ++caseID);
139 cout << bfs_box() << endl << endl;
140 }
141 return 0;
142 }
二、http://www.cnblogs.com/Missa/archive/2012/10/07/2714435.html
1 #include <iostream>
2 #include <cstring>
3 #include <cstdio>
4 #include <algorithm>
5 #include <queue>
6 #include <string>
7
8 using namespace std;
9
10 #define MAXN 22
11 char P[4] = { ‘N‘, ‘S‘, ‘W‘, ‘E‘ };
12 char M[4] = { ‘n‘, ‘s‘, ‘w‘, ‘e‘ };
13 int R, C;
14 int dir[4][2] = { -1, 0, 1, 0, 0, -1, 0, 1 };//之前当成坐标轴里x,y坐标来算，怎么都不对。后来发现原来x,y是行数和列数。x-1代表到上一行去，即N。
15 char map[MAXN][MAXN];
16 struct point
17 {
18 int x, y;
19 int p_x, p_y;//当前状态person所在的地方
20 string ans;
21 };
22 bool isok(int x, int y)
23 {
24 if (x >= 0 && x < R && y >= 0 && y < C && map[x][y] != ‘#‘)
25 return true;
26 return false;
27 }
28 string tmp;
29 bool bfs_person(point en, point cu)
30 {
31 tmp = "";
32 point st;
33 st.x = en.p_x;
34 st.y = en.p_y;
35 st.ans = "";
36 queue<point>q;
37 bool vis[MAXN][MAXN];
38 memset(vis, 0, sizeof(vis));
39 while (!q.empty())
40 q.pop();
41 q.push(st);
42 while (!q.empty())
43 {
44 point cur, next;
45 cur = q.front();
46 q.pop();
47 if (cur.x == en.x && cur.y == en.y)
48 {
49 tmp = cur.ans;
50 return true;
51 }
52 for (int i = 0; i < 4; i++)
53 {
54 next = cur;
55 next.x = cur.x + dir[i][0];
56 next.y = cur.y + dir[i][1];
57 if (!isok(next.x, next.y)) continue;
58 if (next.x == cu.x && next.y == cu.y) continue;//cu.x,cu.y is the location of the box.
59 if (vis[next.x][next.y]) continue;//来过的地方就不能在来了？？？？？？？莫非bfs都是这样？
60 vis[next.x][next.y] = 1;
61 next.ans = cur.ans + M[i];
62 //cout << "M[i] "<<M[i] << endl;
63 //cout << "cur.ans " << cur.ans << endl;
64 q.push(next);
65 }
66 }
67 return false;
68 }
69 string bfs_box()
70 {
71 bool vis[MAXN][MAXN][4];//某点四个方向是否访问！！0==N,1==S,2==W,3==E
72 point st;
73 st.x = st.y = -1;
74 st.p_x = st.p_y = -1;
75 st.ans = "";
76 for (int i = 0; i < R && (st.x == -1 || st.p_x == -1); i++)
77 for (int j = 0; j < C && (st.x == -1 || st.p_x == -1); j++)
78 if (map[i][j] == ‘B‘)
79 {
80 st.x = i;
81 st.y = j;
82 map[i][j] = ‘.‘;
83 }
84 else if (map[i][j] == ‘S‘)
85 {
86 st.p_x = i;
87 st.p_y = j;
88 map[i][j] = ‘.‘;
89 }
90 //----------------------------------------
91 //cout<<"st.x="<<st.x<<" st.y="<<st.y<<" st.p_x="<<st.p_x<<" st.p_y="<<st.p_y<<endl;
92 //----------------------------------------
93 queue<point> q;
94 while (!q.empty())
95 q.pop();
96 q.push(st);
97 memset(vis, 0, sizeof(vis));
98 while (!q.empty())
99 {
100 point cur = q.front(); q.pop();
101 //----------------------------------------
102 // cout<<"cur.x="<<cur.x<<" cur.y="<<cur.y<<" cur.p_x="<<cur.p_x<<" cur.p_y="<<cur.p_y<<endl;
103 // cout<<"-----------------------------\n";
104 //----------------------------------------
105 point next, pre;
106 if (map[cur.x][cur.y] == ‘T‘)
107 return cur.ans;
108 for (int i = 0; i < 4; i++)
109 {
110 next = cur;
111 next.x = cur.x + dir[i][0];
112 next.y = cur.y + dir[i][1];
113 if (!isok(next.x, next.y))
114 continue;
115 if (vis[next.x][next.y][i])
116 continue;
117 pre = cur;
118 switch (i)
119 {
120 case 0: pre.x = cur.x + 1; break;
121 case 1: pre.x = cur.x - 1; break;
122 case 2: pre.y = cur.y + 1; break;
123 case 3: pre.y = cur.y - 1; break;
124 }
125 if (!bfs_person(pre, cur))//搜寻人是否能走到特定的位置
126 continue;
127 vis[next.x][next.y][i] = 1;
128 next.ans = cur.ans + tmp;
129 next.ans = next.ans + P[i];
130 cout << "P[i] " << P[i] << endl;
131 cout <<"cur--"<< cur.x << "," << cur.y << ";" << cur.p_x << "," << cur.p_y << endl;
132 cout <<"next--" << next.x << "," << next.y << ";" << next.p_x << "," << next.p_y << endl;
133 next.p_x = cur.x; next.p_y = cur.y;
134 q.push(next);
135 }
136 }
137 return "Impossible.";
138 }
139
140 int main()
141 {
142 int cas = 1;
143 while (scanf("%d%d", &R, &C) && (R + C))
144 {
145 getchar();
146 for (int i = 0; i < R; i++)
147 gets(map[i]);
148
149 //---------------------------------------
150 // for(int i=0;i<R;i++)
151 // cout<<map[i]<<endl;
152 //----------------------------------------
153
154 printf("Maze #%d\n", cas++);
155 //printf("%s\n",bfs_box());
156 cout << bfs_box() << endl << endl;
157 }
158 return 0;
159 }
时间： 2024-08-10 11:55:57