HDU 1372 Knight Moves （bfs）

Posted 2020-08-12 风中的簌雨

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1372

Knight Moves

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 10372    Accepted Submission(s): 6105

Problem 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 file 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.

 

题目大意：在一个棋盘上（象棋），水平方向a--h竖直方向1--8，每组样例给定两个坐标，求象棋中的 ‘马’ 至少需要几步能够从位置一到达位置二。

解题思路：广搜，因为“马走日” 所以马在一个位置上最多能够走八个位置，定义一个八个位置的数组，每次搜索八个位置即可。

AC代码：

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <iostream>
 4 #include <algorithm>
 5 #include <stack>
 6 #include <queue>
 7 using namespace std;
 8 int f[10][10];
 9 int a[8][2] = {{-2,1},{-1,2},{1,2},{2,1},{2,-1},{1,-2},{-1,-2},{-2,-1}}; //“马走日”所能够到达的八个位置 
10 int change(char ch)  //将a--h转换成对应的1--8 
11 {
12     if (ch == ‘a‘)
13         return 1;
14     if (ch == ‘b‘)
15         return 2;
16     if (ch == ‘c‘)
17         return 3;
18     if (ch == ‘d‘)
19         return 4;
20     if (ch == ‘e‘)
21         return 5;
22     if (ch == ‘f‘)
23         return 6;
24     if (ch == ‘g‘)
25         return 7;
26     if (ch == ‘h‘)
27         return 8;
28 }
29 void bfs(int x,int y,int aa,int b)  //广搜 
30 {
31     memset(f,0,sizeof(f));
32     queue <int > q;  //也可以定义成一个结构体，这样可以少定义一个队列 
33     queue <int > p;
34     q.push(x);
35     p.push(y);
36     f[q.front()][p.front()] = 1;
37     if (x == aa && y == b)  //如果第一个位置和第二个位置相同直接结束 
38         return ;
39     while (!q.empty())  
40     {
41         int x1 = q.front();
42         int y1 = p.front();
43         int ans = f[x1][y1];
44         for (int i = 0; i < 8; i ++)  //以此判断八个位置 
45         {
46             int x2 = x1 + a[i][0];
47             int y2 = y1 + a[i][1];
48             if (x2>0&&x2<=8&&y2>0&&y2<=8&&f[x2][y2]==0)  //注意边界、已经找过的位置不用再找 
49             {
50                 q.push(x2);
51                 p.push(y2);
52                 f[x2][y2] = ans+1;
53             }
54             if (x2 == aa && y2 == b)
55                 return ;
56         }
57         q.pop();
58         p.pop();
59     }
60 }
61 int main ()
62 {
63     char ch1[5],ch2[5];
64     int x,y,a,b;
65     while (scanf("%s",ch1)!=EOF)
66     {
67         scanf("%s",ch2);
68         x = ch1[0]-‘a‘+1;
69         a = ch2[0]-‘a‘+1;
70         y = ch1[1] - ‘0‘;
71         b = ch2[1] - ‘0‘;
72         bfs(x,y,a,b);
73         printf("To get from %s to %s takes %d knight moves.\n",ch1,ch2,f[a][b]-1);
74     }
75     return 0;
76 }