【HDOJ】1885 Key Task

状态压缩+BFS，一次AC。

/* 1885 */
#include <iostream>
#include <queue>
#include <cstring>
#include <cstdio>
#include <cstdlib>
using namespace std;

#define MAXN 105

bool visit[MAXN][MAXN][16];

typedef struct node_t {
    int x, y, t, k;
    node_t() {}
    node_t(int xx, int yy, int tt, int kk) {
        x = xx; y = yy; t = tt; k = kk;
    }
} node_t;

int n, m;
node_t beg;
char map[MAXN][MAXN];
int dir[4][2] = {
    -1,0,1,0,0,-1,0,1
};

inline bool check(int x, int y) {
    return x<0 || x>=n || y<0 || y>=m;
}

int bfs() {
    int i, j, k;
    int x, y, t;
    node_t nd;
    queue<node_t> Q;
    
    memset(visit, false, sizeof(visit));
    visit[beg.x][beg.y][beg.k] = true;
    Q.push(beg);
    
    while (!Q.empty()) {
        nd = Q.front();
        Q.pop();
        t = nd.t + 1;
        for (i=0; i<4; ++i) {
            x = nd.x + dir[i][0];
            y = nd.y + dir[i][1];
            if (check(x, y) || map[x][y]=='#')
                continue;
            if (map[x][y] == 'X')
                return t;
            k = nd.k;
            if (map[x][y]>='A' && map[x][y]<='D') {
                j = map[x][y] - 'A';
                if ((nd.k & (1<<j)) == 0)
                    continue;
            } else if (map[x][y]>='a' && map[x][y]<='d') {
                j = map[x][y] - 'a';
                k |= (1<<j);
            }
            if (visit[x][y][k])
                continue;
            visit[x][y][k] = true;
            Q.push(node_t(x, y, t, k));
        }
    }
    
    return -1;
}

int main() {
    int i, j, k;
    
    #ifndef ONLINE_JUDGE
        freopen("data.in", "r", stdin);
        freopen("data.out", "w", stdout);
    #endif
    
    beg.k = beg.t = 0;
    while (scanf("%d%d",&n,&m)!=EOF && (n||m)) {
        for (i=0; i<n; ++i) {
            scanf("%s", map[i]);
            for (j=0; j<m; ++j) {
                if (map[i][j] == '*') {
                    beg.x = i;
                    beg.y = j;
                } else if (map[i][j] == 'Y') {
                    map[i][j] = 'A';
                } else if (map[i][j] == 'R') {
                    map[i][j] = 'C';
                } else if (map[i][j] == 'G') {
                    map[i][j] = 'D';
                } else if (map[i][j] == 'y') {
                    map[i][j] = 'a';
                } else if (map[i][j] == 'r') {
                    map[i][j] = 'c';
                } else if (map[i][j] == 'g') {
                    map[i][j] = 'd';
                } 
            }
        }
        k = bfs();
        if (k < 0)
            puts("The poor student is trapped!");
        else
            printf("Escape possible in %d steps.
", k);
    }
    
    return 0;
}