Question

private int array[][] = new int[5][5];

private void arrayIteration(){
    for(int i = 0; i < array.length; i++){
        for(int j = 0; j < array.length; j++){
            array[i][j] = 10;
        }
    }
}

Can I change the iteration method to recursive one that does the same task?

Edit (this is what I’ve tried but it’s just playing with what I want to do):

private void arrayRecursion(){
    if(){
        array[i][i] = 10;  // Base
        return;
    }
    for(int i = 0; i < array.length; i++){
        arrayRecursion();
    }
}

Answer 1

Here’s one way you could do it. Basically you start in the 0,0 corner and set it to the value. Then you do 0,1 and 1,0. 0,1 will set, and do 1,1 and 1,2. 1,0 will set and do 2,0 and 1,1. Note that 1,1 just got hit twice – that’s fine because it’s overwriting what it did before. When it hits a ‘wall’ it stops (this means if the [3] array was null, [4] wouldn’t get hit) but that isn’t a problem for arrays allocated with new int[x][y] notation.

class Sandbox {
    public static void main(String[] args) {
        int[][] test = new int[5][5];
        recursiveAssign(test,10);
        int numThatAreTen = 0;
        for(int i = 0; i < 5; i++) {
            for(int j = 0; j < 5; j++) {
                if(test[i][j] == 10) numThatAreTen++;
            }
        }
        System.out.println(numThatAreTen);
    } // main

    static void recursiveAssign(int[][] arr, int value) {
        recursiveAssign0(arr,value,0,0);
    } // recursiveAssign

    static private void recursiveAssign0(int[][] arr, int value, int x, int y) {
        if(arr != null && x < arr.length && arr[x] != null && y < arr[x].length) {
            arr[x][y] = value;
            // now go down, and across
            recursiveAssign0(arr,value,x+1,y);
            recursiveAssign0(arr,value,x,y+1);
        } 
    } // recursiveAssign0

} // Sandbox

which prints the expected 25

C:\Documents and Settings\glowcoder\My Documents>javac Sandbox.java

C:\Documents and Settings\glowcoder\My Documents>java Sandbox
25

C:\Documents and Settings\glowcoder\My Documents>