第一次用剪枝

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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;}