http://acm.hdu.edu.cn/showproblem.php?pid=1010
#include<iostream>
using namespace std;
char gra[8][8];
bool mark[8][8];
int m,n,t,ok;
int si,sj,ei,ej;
 int dir[4][2]= {-1,0,1,0,0,-1,0,1};

int fun(int a,int b)
  {
if(a>b)
return a-b;
else
return b-a;
}

void dfs(int i,int j,int step)
  {
int k,p,q;
if(ok == 1)
return ;
if(step == t)
 {
if(i == ei && j == ej)
ok = 1;
return ;
}
k = fun(i,ei) + fun(j,ej) ;
if(step + k > t) //最快的时间都不能走到,肯定完蛋了
return ;
if(k % 2 != (t-step) % 2)//if((t - step - k) & 1) //奇偶剪枝
return ;
 /**//**//**//*
1 1 1 1 1 1
1 0 1 1 1 1
1 1 1 1 1 1
1 1 1 1 1 1
1 1 1 1 0 1
两个0之间的坐标之差为6,是偶数,只能走偶数步才能到达
*/
for(k=0;k<4;k++)
 {
p = i + dir[k][0];
q = j + dir[k][1];
if(p>=0 && p<m && q>=0 && q<n && gra[p][q]!='X' && mark[p][q] == 0)
 {
mark[p][q] = 1;
dfs(p,q,step+1);
mark[p][q] = 0;
}
}
}
int main()
  {
while(cin>>m>>n>>t && m+n+t)
 {
int i,j,walls=0;
for(i=0;i<m;i++)
for(j=0;j<n;j++)
 {
cin>>gra[i][j];
if(gra[i][j] == 'S')
 {
si = i;
sj = j;
}
else if(gra[i][j] == 'D')
 {
ei = i;
ej = j;
}
else if(gra[i][j] == 'X')
walls++;
mark[i][j] = 0;
}
if(n*m-walls<=t)
 {
cout<<"NO"<<endl;
continue;
}
ok = 0;
mark[si][sj] = 1;
dfs(si,sj,0);
if(ok == 1)
cout<<"YES"<<endl;
else
cout<<"NO"<<endl;
}
return 0;
}
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