Move Zeroes LeetCode Interview Question (Explained Simply)

The title of this LeetCode questions is very ambiguous and does not do a great job explaining what it actually does.

All this interview question is asking you to do is move the zeros to the end of an array. That’s it.

Before:

After:

• Key point: The elements don’t have to be sorted. All non-zero elements must retain the original value.

2-Pointer Step-By-Step (In-Place)

• Given that we are required to transform the array in-place, first we create read and write pointers using two pointer method.
• Loop through array

• Check if reader finds a non-zero. If non-zero is found, swap writer with reader value.

• Increment writer

• If zero is found, do not swap, don’t increment writer, and just increment reader

class Solution {
    public void moveZeroes(int[] nums) {
        //Declare two pointer
        int read = 0;
        int write = 0;
        //Loop thru
        while(read < nums.length){
            //If non-zero number
            if(nums[read] != 0){
                //Swap
                int temp = nums[reader];
                nums[reader] = nums[writer];
                nums[writer] = temp;
                //Increment write
                writer++;
            }
            //Increment reader regardless
            reader++;
        }
    }
}