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poj2243

2024-07-06 17:09:41   224人阅读

题目链接：

http://poj.org/problem?id=2243

题目：

Knight Moves
Time Limit: 1000MS Memory Limit: 65536K
Total Submissions: 10932 Accepted: 6171

Description

A friend of you is doing research on the Traveling Knight Problem (TKP) where you are to find the shortest closed tour of knight moves that visits each square of a given set of n squares on a chessboard exactly once. He thinks that the most difficult part of the problem is determining the smallest number of knight moves between two given squares and that, once you have accomplished this, finding the tour would be easy.
Of course you know that it is vice versa. So you offer him to write a program that solves the "difficult" part.

Your job is to write a program that takes two squares a and b as input and then determines the number of knight moves on a shortest route from a to b.

Input

The input will contain one or more test cases. Each test case consists of one line containing two squares separated by one space. A square is a string consisting of a letter (a-h) representing the column and a digit (1-8) representing the row on the chessboard.

Output

For each test case, print one line saying "To get from xx to yy takes n knight moves.".

Sample Input

e2 e4
a1 b2
b2 c3
a1 h8
a1 h7
h8 a1
b1 c3
f6 f6

Sample Output

To get from e2 to e4 takes 2 knight moves.
To get from a1 to b2 takes 4 knight moves.
To get from b2 to c3 takes 2 knight moves.
To get from a1 to h8 takes 6 knight moves.
To get from a1 to h7 takes 5 knight moves.
To get from h8 to a1 takes 6 knight moves.
To get from b1 to c3 takes 1 knight moves.
To get from f6 to f6 takes 0 knight moves.

Source

Ulm Local 1996
这道题目是搜索的入门提。。

我用两种方法写了一下。。。

bfs版本：

#include<cstdio>
#include<queue>
#include <vector>
#include<iostream>
#include<cstring>
#include<algorithm>
const int maxn=10;
using namespace std;
bool vis[maxn][maxn];
int move[8][2]={{-1,2},{1,2},{-1,-2},{1,-2},{-2,1},{2,1},{-2,-1},{2,-1}};
int step[maxn][maxn];
struct Map
{
    int x,y;
};


int check(int x,int y)
{
    if(x>=1&&y>=1&&y<=8&&x<=8)
        return 1;
    return 0;
}

int bfs(int sx,int sy,int ex,int ey)
{
    queue<Map>q;
    Map a;
    a.x=sx;
    a.y=sy;
    q.push(a);
    vis[sx][sy]=true;
    while(!q.empty())
    {
        Map temp=q.front();
        q.pop();
        for(int i=0;i<8;i++)
        {
            int tx=temp.x+move[i][0];
            int ty=temp.y+move[i][1];
            if(check(tx,ty)&&!vis[tx][ty])
            {
               step[tx][ty]=step[temp.x][temp.y]+1;
               vis[tx][ty]=true;
               if(tx==ex&&ty==ey)
                   return step[ex][ey];
               Map tmp;
               tmp.x=tx;
               tmp.y=ty;
               q.push(tmp);
            }
        }
    }
}

int main()
{
    int sx,sy,ex,ey;
    char s,s1,c;
    while(scanf("%c%d%c%c%d",&s,&sy,&c,&s1,&ey)!=EOF)
    {
       memset(vis,false,sizeof(vis));
       memset(step,0,sizeof(step));
       sx=s-'a'+1;
       ex=s1-'a'+1;
       step[sx][sy]=0;
       if(sx==ex&&sy==ey)
          printf("To get from %c%d to %c%d takes %d knight moves.\n",s,sy,s1,ey,0);
       else
       printf("To get from %c%d to %c%d takes %d knight moves.\n",s,sy,s1,ey,bfs(sx,sy,ex,ey));
       getchar();
    }
    return 0;
}

Dfs版本的：

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdlib>
#define INF 0x3f3f3f3f
const int maxn=10;
using namespace std;
bool vis[maxn][maxn];
int step[maxn][maxn];
int ans,ex,ey;
int dx[8]={-1,-1,1,1,2,2,-2,-2};
int dy[8]={2,-2,2,-2,1,-1,1,-1};


void dfs(int sx,int sy,int depth)
{
   if(sx<1||sy<1||sx>8||sy>8||depth>=ans)
        return;
   if(sx==ex&&sy==ey)
   {
       ans=min(ans,depth);
       return;
   }
   if(!vis[sx][sy])
   {
       vis[sx][sy]=true;
       step[sx][sy]=depth;
   }
   else
   {
       if(step[sx][sy]<=depth)
           return;
       step[sx][sy]=depth;
   }
   for(int i=0;i<8;i++)
   {
       int tx=sx+dx[i];
       int ty=sy+dy[i];
       dfs(tx,ty,depth+1);
   }
}


int main()
{
    char s,s1,c;
    int sx,sy;
    while(scanf("%c%d%c%c%d",&s,&sy,&c,&s1,&ey)!=EOF)
    {
       memset(vis,false,sizeof(vis));
       memset(step,INF,sizeof(step));
       sx=s-'a'+1;
       ex=s1-'a'+1;
       ans=10000;
       dfs(sx,sy,0);
       printf("To get from %c%d to %c%d takes %d knight moves.\n",s,sy,s1,ey,ans);
       getchar();
    }
    return 0;
}



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