hdu -1372 Knight Moves(BFS)

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.

题意：给出骑士的骑士位置和目标位置，计算骑士要走多少步

思路：国际象棋中，骑士是在一个3*2的格子中进行对角线移动，知道骑士最多可以朝八个方向移动，朝8个方向进行BFS即可.

#include <stdio.h>
#include <string.h>
#include <queue>
using namespace std;
     
int step;
int mv[][2] = {-2,1,-1,2,1,2,2,1,2,-1,1,-2,-1,-2,-2,-1};//骑士移动的8个方位
int vis[10][10], ex, ey;
char s1[5], s2[5];
     
struct node{
    int x, y, step;
};
     
int check(int x, int y)
{
    if(x<0 || y<0 || x>=8 || y>=8 || vis[x][y])
    	return 1;
    return 0;
}
     
int bfs()
{
    queue<node> Q;
    node p, next, q;
    p.x = s1[0] - 'a';
    p.y = s1[1] - '1';
    p.step = 0;
    ex = s2[0] - 'a';
    ey = s2[1] - '1';
    memset(vis, 0, sizeof vis);
    vis[p.x][p.y] = 1;
    Q.push(p);
    while(!Q.empty())
    {
        q = Q.front();
        Q.pop();
        if(q.x == ex && q.y == ey)
        	return q.step;
        for(int i = 0; i < 8; i++)
        {
            next.x = q.x+mv[i][0];
            next.y = q.y+mv[i][1];
            if(next.x == ex && next.y == ey)
            	return q.step+1;
            if(check(next.x,next.y))
                continue;
            next.step = q.step+1;
            vis[next.x][next.y] = 1;
            Q.push(next);
        }
    }
    return 0;
}
     
int main()
{
    while(~scanf("%s%s", s1, s2))
    {
        printf("To get from %s to %s takes %d knight moves.\n", s1, s2, bfs());
    }
    return 0;
}