HDOJ_ACM_Tempter of the Bone

4 4 5
S.X.
..X.
..XD
....
3 4 5
S.X.
..X.
...D
0 0 0

NO
YES

#include <stdio.h>
#include <math.h>
#define N 7
#define M 7
int dx[4]={0,1,0,-1};
int dy[4]={1,0,-1,0};
char map[N + 5][M +5];
int n, m, t, flag, desx, desy;
void DFS(int sx, int sy, int step)
{
int i, nx, ny, temp;
//the exit condition
if (flag == 1)
return;
//pruning stategy, one is shortest path, the other is odd-even pruning
temp = (t - (step - 1)) - abs(desx - sx) - abs(desy - sy);
if (temp < 0 || temp & 1)
return;
for (i = 0; i < 4; i++)
{
nx = sx + dx[i];
ny = sy + dy[i];
//out of index
if (nx < 0 || nx >= n || ny < 0 || ny >= m)
continue;
//find it
if (map[nx][ny] == 'D' && step == t)
{
flag = 1;
return;
}
//recursion
if (map[nx][ny] == '.')
{
map[nx][ny] = 'X';
DFS(nx, ny, step + 1);
map[nx][ny] = '.';
}
}
return ;
}
int main()
{
int i, j, sx, sy, countP;
while (scanf("%d %d %d",&n, &m, &t) != EOF && (n || m || t))
{
countP = 0;
flag = 0;
for (i = 0; i < n; i++)
{
scanf("%s", map[i]);
for (j = 0; j < m; j++)
{
if (map[i][j] == 'S')
{
sx = i;
sy = j;
}
if (map[i][j] == 'D')
{
desx = i;
desy = j;
}
if (map[i][j] == '.')
countP++;
}
}
//pruning stategy
if (countP + 1 < t)
{
puts("NO");
continue;
}
DFS(sx, sy, 1);
if (flag == 1)
puts("YES");
else
puts("NO");

}
return 0;
}