http://www.geeksforgeeks.org/minimum-steps-reach-target-knight/
Given a square chessboard of N x N size, the position of Knight and position of a target is given. We need to find out minimum steps a Knight will take to reach the target position.

Apply Dfs and a cache array (to mark visit or not) to search through all the possible ways and find the min steps.

is_outrange --is--> return infinite num
|no
|
is_visited --is--> return infinite num
|no
|
one step forward
|
|
if reach the target:
return the steps so far
else:
keep moving, try 4 directions and get minSearchSteps for 4 directions
U
D
L
R
return the min(U,D,L,R)

tricky part
infinite number for the illegal or visited location.
clear the visited mark when return.

public class Chess_Board {
    private static boolean is_visited(int kx, int ky, int[][] visited) {
        if (visited[kx][ky] == 1) {
            return true;
        }

        return false;
    }

    private static boolean is_outrange(int kx, int ky, int size) {
        if (kx < 0 || ky < 0 || kx >= size || ky >= size) {
            return true;
        }

        return false;
    }

    public static void main(String[] args) {
        int[][] visited_arr = new int[5][5];
        int[][] board = {{0,0,0,0,1},{0,0,0,0,0},{0,0,2,0,0},{0,0,0,0,0},{0,0,0,0,0}};

        System.out.println(minSearchSteps(board, 1, 2, 0, 4, visited_arr, -1));
    }

    private static int minSearchSteps(int[][] board, int kx, int ky, int tx, int ty, int[][] visited, int pre_steps) {
        if (is_outrange(kx, ky, board.length)) {
            return Integer.MAX_VALUE;
        }

        if (is_visited(kx, ky, visited)) {
            return Integer.MAX_VALUE;
        }

        pre_steps += 1;

        //  find it
        if (kx == tx && ky == ty) {
            return pre_steps;
        }

        visited[kx][ky] = 1;



        System.out.println("now kx: " + kx + " ky: " + ky + " steps: " + pre_steps);

        //  not found, keep moving
        int leftMinSteps = minSearchSteps(board, kx - 1, ky, tx, ty, visited, pre_steps);
        int rightMinSteps = minSearchSteps(board, kx + 1, ky, tx, ty, visited, pre_steps);
        int upMinSteps = minSearchSteps(board, kx, ky - 1, tx, ty, visited, pre_steps);
        int downMinSteps = minSearchSteps(board, kx, ky + 1, tx, ty, visited, pre_steps);

        System.out.println("left: " + leftMinSteps);
        System.out.println("right: " + rightMinSteps);
        System.out.println("up: " + upMinSteps);
        System.out.println("down: " + downMinSteps);

        visited[kx][ky] = 0;

        return Math.min(Math.min(leftMinSteps, rightMinSteps), Math.min(upMinSteps, downMinSteps));
    }
}