【HDOJ】1813 Escape from Tetris

bfs预处理一点到边界的最小距离，IDA*求出可行方案。注意按字典序初始化dir数组。并且存在中间点全为1，边界含0的可能性（wa了很多次）。此时不输出任何命令。

/* 1813 */
#include <iostream>
#include <queue>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cstdlib>
using namespace std;

#define MAXN 80
#define INF  0xffffff

int n, m;
char ops[4][6] = {
    "east",
    "north",
    "south",
    "west"
};
int op[1005];
int x[MAXN], y[MAXN];
int dis[9][9];
int visit[9][9];
char map[9][9];
int dir[4][2] = {
    0,1,-1,0,1,0,0,-1
};

inline bool isEnd(int x, int y) {
    return x==0 || x==n-1 || y==0 || y==n-1;
}

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

int bfs(int x, int y) {
    int xx, yy;
    int i, j, k;
    queue<int> Q;
    
    k = 10*x + y;
    Q.push(k);
    memset(visit, -1, sizeof(visit));
    visit[x][y] = 0;
    
    while (!Q.empty()) {
        k = Q.front();
        Q.pop();
        x = k/10;
        y = k%10;
        for (i=0; i<4; ++i) {
            xx = x + dir[i][0];
            yy = y + dir[i][1];
            if (map[xx][yy]=='1' || visit[xx][yy]>=0)
                continue;
            visit[xx][yy] = visit[x][y]+1;
            if (isEnd(xx, yy))
                return visit[xx][yy];
            k = 10*xx + yy;
            Q.push(k);
        }
    }
    return 0;
}

bool dfs(int d, int *px, int *py) {
    int mmax = -1;
    int x[MAXN], y[MAXN];
    int i, j, k;
    
    for (i=0; i<m; ++i)
        mmax = max(mmax, dis[px[i]][py[i]]);
    if (mmax > d)
        return false;
    if (d == 0)
        return true;
    
    for (i=0; i<4; ++i) {
        op[d] = i;
        for (j=0; j<m; ++j) {
            x[j] = px[j] + dir[i][0];
            y[j] = py[j] + dir[i][1];
            if (isEnd(px[j], py[j]) || map[x[j]][y[j]]=='1') {
                x[j] = px[j];
                y[j] = py[j];
            }
        }
        if (dfs(d-1, x, y))
            return true;
    }
    return false;
}

int main() {
    int t = 0;
    int i, j, k;
    
    #ifndef ONLINE_JUDGE
        freopen("data.in", "r", stdin);
        freopen("data.out", "w", stdout);
    #endif
    
    while (scanf("%d",&n) != EOF) {
        m = 0;
        for (i=0; i<n; ++i)
            scanf("%s", map[i]);
        for (i=0; i<n; ++i) {
            for (j=0; j<n; ++j) {
                if (map[i][j] == '1') {
                    dis[i][j] = INF;
                } else {
                    if (isEnd(i, j)) {
                        dis[i][j] = 0;
                    } else {
                        dis[i][j] = bfs(i, j);
                        x[m] = i;
                        y[m] = j;
                        ++m;
                    }
                }
            }
        }
        if (t++)
            printf("
");
        if (m) {
            for (i=1; ; ++i) {
                if (dfs(i, x, y))
                    break;
            }
            for (j=i; j>0; --j)
                printf("%s
", ops[op[j]]);
        }
    }
    
    return 0;
}