DFS 专题 Tempter of the Bone

这道题的剪枝：奇偶性，曼哈顿距离类型的。不剪会超时。

# include <cstdio>
# include <cstring>

using namespace std;

# define N 7 + 3
# define ABS(x) (((x)>0)?(x):(-(x)))

int si, sj, gi, gj;
int n, m, T;
char g[N][N];
bool vis[N][N];
bool finished;

const int dir[][2] = {{0,1}, {1,0}, {0,-1}, {-1,0}};

void dfs(int x, int y, int t)
{
    int tmp = ABS(x-gi)+ABS(y-gj);
    if (tmp > t) return;
    if (tmp%2 != t%2) return ;
    if (t == 0) finished = (x == gi && y == gj);
    else for (int d = 0; d < 4; ++d)
    {
        int nx = x + dir[d][0], ny = y + dir[d][1];
        if (1<=nx&&nx<=n && 1<=ny&&ny<=m && g[x][y]!='X' && vis[nx][ny]==false)
        {
            vis[nx][ny] = true;
            dfs(nx, ny, t-1);
            if (finished) return ;
            vis[nx][ny] = false;
        }
    }
}

void init(void)
{
    int in;

    in = 0;
    for (int i = 1; i <= n; ++i)
    {
        scanf("%s", g[i]+1);
        memset(vis[i], false, sizeof(vis[0][0])*(m+1));
        for (int j = 1; in<2 && j <= m; ++j)
            if(g[i][j] == 'S') si = i, sj = j, ++in;
            else if (g[i][j] == 'D') gi = i, gj = j, ++in;
    }
}

void solve(void)
{
    finished = false;
    vis[si][sj] = true, dfs(si, sj, T);
    puts(finished ? "YES":"NO");
}

int main()
{
    while (scanf("%d%d%d", &n, &m, &T), n || m || T)
    {
        init();
        solve();
    }

    return 0;
}

/**/