第一次用剪枝

HDOJ 1010

#include <cstdio>
#include <cmath>
using namespace std;

int n, m, t, sx, sy, ex, ey;
char maze[8][8];
int dir[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
bool escape = false;

int least_distance(int x, int y)
{
    return abs(x - ex) + abs(y - ey);
}


void DFS(int x, int y, int step)
{

    if (x < 1 || y < 1 || x > n || y > m)
        return;

    if (x==ex && y==ey && step==t)
    {
        escape = true;

    }

    if (escape)
        return;


    int temp = (t - step) - least_distance(x, y);
    if (temp < 0 || temp % 2 == 1)
        return;

    for (int i = 0; i < 4; ++i)
    {
        int xt = x + dir[i][0];
        int yt = y + dir[i][1];

        if (maze[xt][yt] != 'X')
        {
            maze[xt][yt] = 'X';
            DFS(xt, yt, step + 1);
            maze[xt][yt] = '.';
        }
    }
}


int main()
{
    // freopen("in.txt", "r", stdin);
    while(scanf("%d %d %d", &n, &m, &t) && (n + m + t))
    {

        getchar();
        //printf("%d %d %d\n", n, m, t);
        escape = false;
        int wall = 0;
        sx = sy = ex = ey = 0;


        for(int i = 1; i <= n; ++i)
        {
            for(int j = 1; j <= m; ++j)
            {
                scanf("%c", &maze[i][j]);
                //printf("%c", maze[i][j]);

                if(maze[i][j] == 'S')
                {
                    sx = i;
                    sy = j;
                }
                if(maze[i][j] == 'D')
                {
                    ex = i;
                    ey = j;
                }
                if(maze[i][j] == 'X')
                {
                    wall++;
                }

            }
            getchar();
           // printf("\n");
        }
        if(m * n - wall <= t)
        {
            printf("NO\n");
            continue;
        }
        maze[sx][sy] = 'X';
        DFS(sx, sy, 0);
        if(escape)
            printf("YES\n");
        else
            printf("NO\n");
    }
    return 0;
}