how to search elements in a 2d array using recursion

问题

I have a 2d char array and I'm trying to find a specific character using recursion.

public class Test {

char arry [][] = {{'1',' ','B'},
                  {'C','K','M'},
                  {'H','R','P'}
};

public Test(){
    recursion(0,0,arry[0][0]);

}
private void recursion(int row, int col, char c) {
    if(c==' '){
        System.out.print("Location: " + row + " " + col );
    }else
    {
        if(col+1<arry[0].length){
            recursion(row,col,c);
        }
                    //System.out.print(arry[0][1]);

    }

}
public static void main(String[] args) {

    new Test();
}

}

but this is giving me a stack overflow. how can I find an element in a 2d array using recursion.

回答1:

It looks like your if statement isn't being executed properly. You are checking to check if c == " ", though I think you meant it to check if array[row][col]==c. Also, it seems like you never actually increment the values of row and col, so the recursion continuously happens on itself. Since the recursion values never change, and the check can never be true, this will eventually lead to a stackoverflow.

Try something along these lines:

private void recursion(int row, int col, char c) {
    if(array[row][col]==c){
        System.out.print("Location: " + row + " " + col );
    } else {
        if(col+1<array[0].length){
            recursion(row,col+1,c);
        } else if(row + 1<array[1].length){
            recursion(row+1,0,c);
        } else {
            System.out.print("Does not exist");
            //System.out.print(arry[0][1]); 
        }
    }
}

回答2:

You method is calling itself with same values all the time.

recursion(row,col,c);

Update your value then send it to the method again. so it could look for another element in your array

For example:

recursion(row,++col,c);

回答3:

private void recursion(int row, int col, char c) {
if(c==' '){
    System.out.print("Location: " + row + " " + col );
}else
{
    if(col+1<arry[0].length){
        recursion(row,col+1,c);
    }
    else
         recursion(row+1, 0, c)
                //System.out.print(arry[0][1]);

}

}

回答4:

The easiest way to search for a value in a 2D-Array would be to start at (0, 0) and scan through the entire column before advancing to the next row. When a value matches what you are looking for, return that location.

Here is an example.

import java.util.Arrays;

public class Find2D {
    public static int[] search(char[][] arr, char ch, int row, int col) {
        if (arr[row][col] == ch) {
            return new int[] { row, col };
        } else {
            if (col + 1 < arr[0].length) {
                return search(arr, ch, row, col + 1);
            } else if (row + 1 < arr[1].length) {
                return search(arr, ch, row + 1, 0);
            }
        }
        return null;
    }

    public static int[] search(char[][] arr, char ch) {
        return search(arr, ch, 0, 0);
    }

    public static void printr(int[] result) {
        System.out.println("Location: " + Arrays.toString(result));
    }

    public static void main(String[] args) {
        char arr[][] = {
            { '1', ' ', 'B' },
            { 'C', 'K', 'M' },
            { 'H', 'R', 'P' }
        };

        printr(search(arr, arr[0][0])); // [0, 0]
        printr(search(arr, 'M'));       // [1, 2]
        printr(search(arr, 'x'));       // null
    }
}

来源：https://stackoverflow.com/questions/22434762/how-to-search-elements-in-a-2d-array-using-recursion

标签

java

arrays

recursion