這道題是標準的騎士問題，但是當時沒有考慮其實和終止位置相同的情況，所以就浪費了好多時間。好在最後想出來了。

題目：

AC程式碼：

#include <iostream>
#include <queue>
using namespace std;

void jump();
int board[12][12];
int xend;
int yend;

class point
{
public:
    int x;
    int y;
    int number;
};
queue<point> q1;

void init()
{
    for(int i = 2; i < 10; i++)
        for(int j = 2; j < 10; j++)
            board[i][j] = 0;
    for(int i = 0; i < 12; i++)
    {
        board[i][0] = -1;
        board[i][1] = -1;
        board[i][10] = -1;
        board[i][11] = -1;
    }
    for(int i = 2; i < 10; i++)
    {
        board[0][i] = -1;
        board[1][i] = -1;
        board[10][i] = -1;
        board[11][i] = -1;
    }
}

int main()
{
    int b;
    int k = 1;
    init();

    int beg1, beg2, end1, end2;
    cin >> beg1>> beg2;
    cin >> end1 >> end2;
    xend = end1+ 1;
    yend = end2+ 1;
    if (beg1 == end1 && beg2 == end2) {
        cout << 0 << endl;
        return 0;
    }
    point p1;
    p1.x = beg1+1;
    p1.y = beg2+1;
    p1.number = 0;
    q1.push(p1);
    jump();
    if(board[xend][yend] == 0)
    {
        cout << "not reachable" << endl;
    }
    else
    {
        cout << board[xend][yend] << endl;
    }
    return 0;
}

void jump()
{
    while(!q1.empty())
    {
        point p0 = q1.front();
        q1.pop();
        point p1;
        p1.x = p0.x-1;
        p1.y = p0.y-2;
        p1.number = p0.number + 1;
        if(board[p1.x][p1.y] == 0)
        {

            board[p1.x][p1.y] = p1.number;
            q1.push(p1);
        }
        p1.x = p0.x-1;
        p1.y = p0.y+2;
        if(board[p1.x][p1.y] == 0)
        {

            board[p1.x][p1.y] = p1.number;
            q1.push(p1);
        }
        p1.x = p0.x+1;
        p1.y = p0.y-2;
        if(board[p1.x][p1.y] == 0)
        {

            board[p1.x][p1.y] = p1.number;
            q1.push(p1);
        }
        p1.x = p0.x+1;
        p1.y = p0.y+2;
        if(board[p1.x][p1.y] == 0)
        {

            board[p1.x][p1.y] = p1.number;
            q1.push(p1);
        }
        p1.x = p0.x-2;
        p1.y = p0.y-1;
        if(board[p1.x][p1.y] == 0)
        {

            board[p1.x][p1.y] = p1.number;
            q1.push(p1);
        }
        p1.x = p0.x-2;
        p1.y = p0.y+1;
        if(board[p1.x][p1.y] == 0)
        {
            board[p1.x][p1.y] = p1.number;
            q1.push(p1);
        }
        p1.x = p0.x+2;
        p1.y = p0.y-1;
        if(board[p1.x][p1.y] == 0)
        {
            board[p1.x][p1.y] = p1.number;
            q1.push(p1);
        }
        p1.x = p0.x+2;
        p1.y = p0.y+1;
        if(board[p1.x][p1.y] == 0)
        {
            board[p1.x][p1.y] = p1.number;
            q1.push(p1);
        }
    }

}