HDU/HDOJ 2563 統計問題 回溯發DFS

題目連結：http://acm.hdu.edu.cn/showproblem.php?pid=2563

深搜回溯逾時，於是可恥的打了個表，0MS AC了。。

#include<iostream>#include<cstdio>#include<cmath>#include<fstream>using namespace std;int ans[21]={0,3,7,17,41,99,239,577,1393,3363,8119,19601,47321,114243,275807,665857,1607521,3880899,9369319,22619537,54608393};int main(){int c;cin>>c;while(c--){int n;cin>>n;cout<<ans[n]<<endl;}return 0;}

看一下我深搜的思路吧，很簡單的往三個方向搜，做標記：

#include<iostream>#include<cstdio>#include<cmath>#include<fstream>using namespace std;bool maze[25][50];int n,sum;int dir[3][2]={0,1,0,-1,-1,0};void dfs(int x,int y,int step){if(step==n)sum++;else {for(int i=0;i<3;i++){int newx=x+dir[i][0];int newy=y+dir[i][1];if(maze[newx][newy])continue;maze[newx][newy]=1;dfs(newx,newy,step+1);maze[newx][newy]=0;}}}int main(){int c;cin>>c;int ans[25];ans[0]=0;for(n=1;n<=20;n++){memset(maze,0,sizeof(maze));maze[20][20]=1;sum=0;dfs(20,20,0);ans[n]=sum;}ofstream fout;fout.open("file1.txt");for(int i=1;i<=20;i++)fout<<ans[i]<<" ";/*while(c--){cin>>n;cout<<ans[n]<<endl;}*/return 0;}