URAL 1920 Titan Ruins: the Infinite Power of Magic

大意：

有一张N*N的网格，你每次可以走一步，每格只能走一次，有没有一种方法让走了L步后回到一个距原点1步远的格子？ 





没有输出Unsuitable device，否则输出Overwhelming power of magic并输出方案。 

一开始用DFS 奇偶剪枝了还是TLE,

代码如下：

#include<iostream>
#include<cstring>
#include<cmath>
#define N 110
using namespace std;

int n,t,end_i,end_j;
bool visited[N][N],flag,ans;
char map[N][N];
int run[10010][2];
int tem;
int a[4][2]={{-1,0},{1,0},{0,-1},{0,1}};

void DFS(int i,int j,int c)
{
if(flag){ return ;}
    if(c>t) return ;
    if(i<=0||i>n||j<=0||j>n) {return ;}
    if(map[i][j]=='D'&&c==t) {flag=ans=true; return ;}
    int temp=abs(i-end_i)+abs(j-end_j);
    temp=t-temp-c;         //t扣掉还要走的最短步temp 和 已经走过的 c 如果这些步还是奇数直接不满足
    if(temp&1) return ;//奇偶剪枝 奇数return
   for(int k=0;k<4;k++)
    	if(!visited[i+a[k][0]][j+a[k][1]]) //开始进行各个方向的探索 记得回溯，取消之前走的状态
    	{
    	 visited[i+a[k][0]][j+a[k][1]]=true;
    	 DFS(i+a[k][0],j+a[k][1],c+1);
    	 if(flag){cout<<i+a[k][0]<<" "<<j+a[k][1]<<endl;break;}
    	 visited[i+a[k][0]][j+a[k][1]]=false;
    	}
}

int main()
{
    int i,j;
    while(cin>>n>>t)
    {
    	if(t%2!=0||t>n*n){cout<<"Unsuitable device"<<endl;continue;}
    	else cout<<"Overwhelming power of magic"<<endl;
    	cout<<"1 1"<<endl;
    	memset(visited,0,sizeof(visited));

    	        for(i=1;i<=n;i++)
    	        {

    	            for(j=1;j<=n;j++)
    	            {
    	               map[i][j]='.';
    	            }
    	        }
    	        end_i=2;end_j=1;
    	        map[2][1]='D';
    	        visited[1][1]=1;

        ans=flag=false;

       DFS(1,1,1);
//        if(ans) cout<<"YES"<<endl;
//        else cout<<"NO"<<endl;
    }
    return 0;
}

后来是找规律做出来的，根据奇偶分类讨论一下；；

代码写的很烂。。

很多复用的没复用。。

#include<iostream>
#include<cstring>
#include<cmath>
#define N 110
using namespace std;

int n,t,end_i,end_j;
bool visited[N][N],flag,ans;
char map[N][N];
int run[10010][2];
int tem;
int a[4][2]={{-1,0},{1,0},{0,-1},{0,1}};

int main()
{
    int i;int xx,yy,kk;
    while(cin>>n>>t)
    {
    	if(t%2!=0||t>n*n){cout<<"Unsuitable device"<<endl;continue;}
    	else cout<<"Overwhelming power of magic"<<endl;
//    	cout<<"1 1"<<endl;
    	if(n%2==0){
    		if(t<=2*n){
    			for(i=1;i<=t/2;i++){
    				cout<<1<<" "<<i<<endl;
    			}
    			for(i=t/2;i>0;i--){
    			    				cout<<2<<" "<<i<<endl;
    			    			}
    		}
    		else{
    		 kk=t-2*n;
    		 yy=kk/(2*(n-2));
    		 xx=kk%(2*(n-2));
    		for(i=1;i<=n;i++){
    			cout<<"1 "<<i<<endl;
    		}
    		if(xx!=0){
    			int w2=n-2;
    		for( i=2;i<=2+xx/2;i++){
    			cout<<i<<" "<<n<<endl;
    		}
    		for( i=2+xx/2;i>=2;i--){
    		    			cout<<i<<" "<<n-1<<endl;
    		    		}
    		while(yy--){

    	    				for(i=2;i<=n;i++)
    	    					cout<<i<<" "<<w2<<endl;
    	    				for(i=n;i>=2;i--)
    	    				    					cout<<i<<" "<<w2-1<<endl;
    	    				w2-=2;
    	    			}
    		while(w2!=0){

    		    					cout<<"2 "<<w2<<endl;
    		    					cout<<"2 "<<w2-1<<endl;
    		    				w2-=2;
    		    			}
    		}
    		else{
    			int wei;
    			wei=n;
    			while(yy--){

    				for(i=2;i<=n;i++)
    					cout<<i<<" "<<wei<<endl;
    				for(i=n;i>=2;i--)
    				    					cout<<i<<" "<<wei-1<<endl;
    				wei-=2;
    			}
    			while(wei!=0){

    					cout<<"2 "<<wei<<endl;
    					cout<<"2 "<<wei-1<<endl;
    				wei-=2;
    			}
    		}
    		}
    	}
    	else{

    		if(t<=2*n){
    			for(i=1;i<=t/2;i++){
    				cout<<1<<" "<<i<<endl;
    			}
    			for(i=t/2;i>0;i--){
    			    				cout<<2<<" "<<i<<endl;
    			    			}
    		}
    		else if(t<=2*n+2*(n-2)){
    			int er=(t-(2*n))/2;
    			for(i=1;i<=n;i++){
    			    				cout<<1<<" "<<i<<endl;
    			    			}
    			for(i=n;i>=3;i--){
    			    			    				cout<<2<<" "<<i<<endl;
    			    			    			}
    			for(i=2;i<=2+er;i++){
    				cout<<i<<" "<<2<<endl;
    			}
    			for(i=er+2;i>=2;i--){
    			    				cout<<i<<" "<<1<<endl;
    			    			}

    		}
    		else if(t<=(n+n-1+3*(n-2))){
    			int bb=(t-(2*n+2*(n-2)))/2;
    			for(i=1;i<=n;i++){
    			    	cout<<1<<" "<<i<<endl;
    			    			    	}
    			for(i=n;i>=3;i--){
    			    			    	cout<<2<<" "<<i<<endl;
    			    			    			    	}
    			for(i=3;i<=n;i++){
    				cout<<i<<" "<<3<<endl;
    			}
    			cout<<n<<" "<<2<<endl;
    			int x=n,y=1;
    			cout<<x<<" "<<y<<endl;
    			x--;
    			cout<<x<<" "<<y<<endl;

    			while(1){
    				if(x==2&&y==1){break;}
    				if(bb>0&&y==1&&x%2==0){
    					y=2;bb--;
    					cout<<x<<" "<<y<<endl;
    				}
    				else if(y==2&&x%2==0){
    					x--;
    					cout<<x<<" "<<y<<endl;
    				}
    				else if(y==2&&x%2==1){
    					y=1;cout<<x<<" "<<y<<endl;
    				}
    				else if(y==1&&x%2==1){
    					x--;
    					cout<<x<<" "<<y<<endl;
    				}
    				else if(bb<=0&&y==1&&x%2==0){
    					x--;
    					cout<<x<<" "<<y<<endl;
    				}
    			}
    		}
    		else{
    		 kk=t-(n+n-1+3*(n-2));
    		 yy=kk/(2*(n-2));
    		 xx=kk%(2*(n-2));
    		for(i=1;i<=n;i++){
    			cout<<"1 "<<i<<endl;
    		}
    		if(xx!=0){
    			int w21=n-2;
    		for( i=2;i<=2+xx/2;i++){
    			cout<<i<<" "<<n<<endl;
    		}
    		for( i=2+xx/2;i>=2;i--){
    		    			cout<<i<<" "<<n-1<<endl;
    		    		}
    		while(yy--){

    	    				for(i=2;i<=n;i++)
    	    					cout<<i<<" "<<w21<<endl;
    	    				for(i=n;i>=2;i--)
    	    				    					cout<<i<<" "<<w21-1<<endl;
    	    				w21-=2;
    	    			}
    		while(w21!=3){

    		    					cout<<"2 "<<w21<<endl;
    		    					cout<<"2 "<<w21-1<<endl;
    		    				w21-=2;
    		    			}
    		}
    		else{
    			int wei2;
    			wei2=n;
    			while(yy--){

    				for(i=2;i<=n;i++)
    					cout<<i<<" "<<wei2<<endl;
    				for(i=n;i>=2;i--)
    				    					cout<<i<<" "<<wei2-1<<endl;
    				wei2-=2;
    			}
    			while(wei2!=3){

    					cout<<"2 "<<wei2<<endl;
    					cout<<"2 "<<wei2-1<<endl;
    				wei2-=2;
    			}
    		}
    		/*
    		 *
    		 */
    		for(i=2;i<=n;i++){
    		    				cout<<i<<" "<<3<<endl;
    		    			}
    		    			cout<<n<<" "<<2<<endl;
    		    			int x=n,y=1;
    		    			cout<<x<<" "<<y<<endl;
    		    			x--;
    		    			cout<<x<<" "<<y<<endl;

    		    			while(1){
    		    				if(x==2&&y==1){break;}
    		    				if(y==1&&x%2==0){
    		    					y=2;
    		    					cout<<x<<" "<<y<<endl;
    		    				}
    		    				else if(y==2&&x%2==0){
    		    					x--;
    		    					cout<<x<<" "<<y<<endl;
    		    				}
    		    				else if(y==2&&x%2==1){
    		    					y=1;cout<<x<<" "<<y<<endl;
    		    				}
    		    				else if(y==1&&x%2==1){
    		    					x--;
    		    					cout<<x<<" "<<y<<endl;
    		    				}

    		    			}

    		}

    	}

    }
    return 0;
}

有的队也有用DFS过的T T

#include<iostream>
using namespace std;
int n,l,ans;
void dfs(int x,int y,int z){
	if(ans==l) return ;
	if(x>n||y>n) return ;
	if(z==0){
		printf("%d %d\n",x,y);
		ans+=2;
		dfs(x+1,y,0);
		printf("%d %d\n",x,y+1);
		if(n%2==x%2) dfs(x,3,1);
	}
	else if(z==1){
		printf("%d %d\n",x,y);
		ans+=2;
		dfs(x,y+1,1);
		printf("%d %d\n",x-1,y);
		if(x==3&&y%2==0) dfs(x-2,y,2);
	}
	else if(z==2){
		ans+=2;
		printf("%d %d\n",x,y);
		printf("%d %d\n",x,y-1);
	}
}
int main(){
	cin>>n>>l;
	if(l%2==1||n*n<l){
		printf("Unsuitable device\n");
	}
	else{
		printf("Overwhelming power of magic\n");
		printf("1 1\n");
		printf("2 1\n");
		ans=4;
		dfs(3,1,0);
		printf("2 2\n");
		if(ans!=n) dfs(2,3,1);
		printf("1 2\n");
	}
	return 0;
}

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