需要Java代码说明（递归迷宫求解器）

Question

There might come some follow up questions for this (and yes this is homework), but we have to solve a maze in my Java programming class (complete beginner) with using a recursive method. Now my problem is not the actual solving (yet, I am sure it will soon be my problem), but the fact that we have been given a part of the code by the teacher and there is some stuff in it that I have absolutely no clue what it is, or what it means.

Yes, I could ask my teacher, but I really don't like this guy and I am really just trying to learn Java and get some college credit points.

public class MazeSolver {

    public static void main(String[] args) {

        int[][] mArr = {
            {2, 1, 1, 1, 0, 1, 1, 1},
            {1, 1, 0, 1, 0, 1, 1, 0},
            {0, 1, 1, 0, 1, 1, 1, 1},
            {0, 0, 1, 1, 1, 0, 1, 0},
            {1, 0, 0, 0, 1, 0, 1, 1},
            {0, 0, 0, 0, 1, 1, 0, 1},
            {0, 0, 0, 0, 0, 1, 1, 3}
        };

        boolean result = solve(mArr, 0, 0); // i = 0, j = 0: Point of entry in the upper left corner
        String str = (result) ? "" : " nicht";
        System.out.println("Das Labyrinth ist" + str + " loesbar");
    }

        static boolean solve(int[][] mArr, int i, int j) {


        return false;
    }

        static void print(int[][] mArr) {
        System.out.println();
        for (int[] arr : mArr) {
            for (int n : arr) {
                System.out.print(n + " ");
            }
            System.out.println();
        }
        System.out.println();
    }

}

Ok, so my problem is this line: boolean result = solve(mArr, 0, 0); // i = 0, j = 0: Point of entry in the upper left corner .

I am assuming this means that result is the result of the method which I am still to define, but what is (mArr, 0, 0) ? I am guessing that is supposed to give the location in the maze but I thought that a location in an array is ie mArr [0][0] . And how does the program know that 0 and 0 is i and j or is that something that I need to tell it at some point?

Answer 1

solve() calls the method you have defined static boolean solve(int[][] mArr, int i, int j) { . It passes the array, along with i and j to that method. i and j represent the start position. You are correct that the starting position would be mArr[i][j], so inside the solve method, do this.

ie

static boolean solve(int[][] mArr, int i, int j) {
    int startPosValue = mArr[i][j]
    //code to determine return value
}

Answer 2

Let's assume that you can only move right or down, as otherwise it's not possible to solve with those three arguments. Then, the algorithm will be:

static boolean solve(int[][] mArr, int i, int j) {
    if (mArr[i][j] == 3) {
        return true;
    } else {
    try {
        if (arr[i+1][j] == 1 &&solve(mArr, i+1, j))
            return true;
    }catch(IndexOutOfBoundsException e) {};
    try {
        if (arr[i][j+1] == 1 && solve(mArr, i, j+1))
            return true;
    }catch(IndexOutOfBoundsException e) {};
    return false;
}

It'll return true if there is existing path and false otherwise.

How it works?

The signature could be rewritten:

static boolean solve(int[][] mArr, int currentX, int currentY)

It checks if mArr[i][j] is 3 (end). If yes, it returns true . Otherwise it checks if there is a possibility to reach the end by moving right or down.