poj1475

推箱子，嵌套BFS， 比较直白

稍微详细一点的解释见这里

http://www.xuebuyuan.com/304871.html

#include<cstdio>#include<cstring>#include<iostream>#include<queue>using namespace std;#define MAXN 25int dir[4][2] = {-1, 0, 0, -1, 1, 0, 0, 1};int vis_box[MAXN][MAXN], vis_player[MAXN][MAXN];char map[MAXN][MAXN];int r, c, px, py, bx, by;char box_path[5] = "NWSE";char player_path[5] = "nwse";string temp_ans;struct Player{    int x, y;    string path;};struct Box{    int x, y;    int px, py;    string path;};bool ok(int x, int y) {    if(x >= 0 && x < r && y >= 0 && y < c) {        return true;    }    return false;}bool Player_BFS(int sx, int sy, int ex, int ey, int tx, int ty) {    temp_ans = "";    if(ex < 0 || ex >= r || ey < 0 || ey >= c) {        return false;    }    Player start;    start.x = sx;    start.y = sy;    start.path = "";    memset(vis_player, 0, sizeof(vis_player));    vis_player[sx][sy] = 1;    queue<Player>Q;    Q.push(start);    while(!Q.empty()) {        Player hd = Q.front();        Q.pop();        if(hd.x == ex && hd.y == ey) {            temp_ans = hd.path;            return true;        }        for(int i = 0; i < 4; ++ i) {            int x = hd.x + dir[i][0];            int y = hd.y + dir[i][1];            if(x == tx && y == ty) {                continue;            }            if(ok(x, y) && !vis_player[x][y]) {                if(map[x][y] != '#') {                    vis_player[x][y] = 1;                    Player t;                    t.x = x;                    t.y = y;                    t.path = hd.path + player_path[i];                    Q.push(t);                }            }        }    }    return false;}void Box_BFS() {    memset(vis_box, 0, sizeof(vis_box));    Box start;    start.x = bx;    start.y = by;    start.px = px;    start.py = py;    start.path = "";    vis_box[bx][by] = 1;    queue<Box>Q;    Q.push(start);    while(!Q.empty()) {        Box hd = Q.front();        Q.pop();        for(int i = 0; i < 4; ++ i) {            int x = hd.x + dir[i][0];            int y = hd.y + dir[i][1];            if(ok(x, y) && !vis_box[x][y]) {                if(map[x][y] != '#') {                    if(Player_BFS(hd.px, hd.py, hd.x - dir[i][0], hd.y - dir[i][1], hd.x, hd.y)) {                        Box t;                        t.x = x;                        t.y = y;                        t.px = hd.x;                        t.py = hd.y;                        vis_box[x][y] = 1;                        t.path = hd.path + temp_ans + box_path[i];                        if(map[x][y] == 'T') {                            cout << t.path << endl;                            return;                        } else {                            Q.push(t);                        }                    }                }            }        }    }    printf("Impossible.\n");}int main() {    freopen("poj1475.txt", "r", stdin);    int cnt = 0;    while(scanf("%d%d", &r, &c), r) {        for(int i = 0; i < r; ++ i) {            scanf("%s", map[i]);            for(int j = 0; j < c; ++ j) {                if(map[i][j] == 'S') {                    px = i;                    py = j;                }                if(map[i][j] == 'B') {                    bx = i;                    by = j;                }            }        }        printf("Maze #%d\n", ++ cnt);        Box_BFS();        printf("\n");    }    return 0;}