HDU/HDOJ 2563 统计问题 回溯发DFS

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=2563

深搜回溯超时，于是可耻的打了个表，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，很简单的往三个方向搜，做标记：

#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;
}