dfs&&hdu1010奇偶剪枝

很神奇的剪枝條件：奇偶剪枝

用到奇偶剪枝原理：

#include<cstdio>#include<algorithm>#include<cmath>#include<queue>#include<vector>#include<string.h>#include<iostream>using namespace std;int dx[]={1,-1,0,0},dy[]={0,0,-1,1};char Map[7][7];int n,m,t;bool vis[7][7];bool ok;int ex,ey;int dis(int x,int y){ return abs(x-ex)+abs(y-ey);}void dfs(int x,int y,int step){        if(ok)return;          if(Map[x][y]=='D'&&step==t)          {            ok=1;return ;          }          if(step>=t)return;          int tmp=t-step-dis(x,y);          if(tmp<0||tmp%2)return;          for(int i=0;i<4;i++)          {           int xx=x+dx[i];           int yy=dy[i]+y;           if(xx>=0&&n>xx&&yy>=0&&yy<m&&!vis[xx][yy]&&Map[xx][yy]!='X')           {                       vis[xx][yy]=true;            dfs(xx,yy,step+1);            vis[xx][yy]=false;           }          }         }int main(){  int sx,sy,con=0;    while(cin>>n>>m>>t,n+m+t)    { con=0;ok=0;       memset(vis,false,sizeof(vis));       for(int i=0;i<n;i++)           for(int j=0;j<m;j++)           {                cin>>Map[i][j];                if(Map[i][j]=='S')                {sx=i;sy=j;vis[i][j]=1;}//剛開始忘記把起點標記已訪問wa了一次                else if(Map[i][j]=='D')                {                   ex=i;ey=j;                }                else if(Map[i][j]=='X')                {                con++;                }           }           if(n*m-con>t)           {                         dfs(sx,sy,0);           }            if(ok)                printf("YES\n");            else                 printf("NO\n");    } return 0;}