Leetcode 283. Move Zeroes — Striver a2z DSA/Sheet

Problem statement — Given an integer array nums, move all 0's to the end of it while maintaining the relative order of the non-zero elements.

Note that you must do this in-place without making a copy of the array.

Example 1:

Input: nums = [0,1,0,3,12]
Output: [1,3,12,0,0]

Example 2:

Input: nums = [0]
Output: [0]

Constraints:

• 1 <= nums.length <= 104
• -231 <= nums[i] <= 231 - 1

Optimal Approach —

The idea is that we go through the array and gather all zeros on our road.

Let’s take our example:
the first step — we meet 0.
Okay, just remember that now the size of our snowball is 1. Go further.

Next step — we encounter 1. Swap the most left 0 of our snowball with element 1.

Next step — we encounter 0 again!

Our ball gets bigger, now its size = 2.

Next step — 3. Swap again with the most left zero.

Looks like our zeros roll all the time

Next step — 12. Swap again:

We reached finish! Congratulations!

Here’s the code

class Solution {
     public void moveZeroes(int[] nums) {
        int snowBallSize = 0; 
        for (int i=0;i<nums.length;i++){
	        if (nums[i]==0){
                snowBallSize++; 
            }
            else if (snowBallSize > 0) {
	            int t = nums[i];
	            nums[i]=0;
	            nums[i-snowBallSize]=t;
            }
        }
    }
}