Recursion for Coding Interviews in Java/

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Solution Review: Permutations of a String

Solution Review: Permutations of a String

This lesson provides a detailed review of the solution to the challenge of the previous lesson.

We'll cover the following...

Solution: Permutations of a String

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class Solution {
    public static void permutations(char[] array, int length) {
        if (length == 1) {
            System.out.println(array);
            return;
        }
        else {
            for (int i = 0; i < length; i++) {
                swap(array, i, length-1);
                permutations(array, length-1);
                swap(array, i, length-1);
            }
        }
    }  
    
    public static void swap(char[] array, int i, int j) {
        char c;
        c = array[i]; 
        array[i] = array[j]; 
        array[j] = c;
    }
    public static void main( String args[] ) {
        char[] input = {'a', 'b', 'b', 'a'};
        permutations(input, input.length);
    }
}

Understanding the Code

Every recursive code has two methods; the recursive method and the main method.

Driver Method

The recursive method is called within the driver method. Let’s first look at what it does-from lines 25 to 27.

  • An array of characters input is initialized on line 25.

  • The recursive method permutations is called on line 26 which takes in two input parameters: ...