Problem Statement

Given an array nums, write a function to move all 0’s to the end of it while maintaining the relative order of the non-zero elements.

Example

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

Solution (copying to left)

We can keep a index variable which will keep a tab on all non-zero values.

On iteration, we can move each non-zero value to left side.

Code

public void moveZeroes_simple(int[] nums) {
   int left=0;
   
   for (int i=0; i<nums.length; i++) {
      if (nums[i] != 0) {
         nums[left] = nums[i];
         left ++;
      }
   }
   
   //copy zeroes to remaining array
   for (int i=left; i<nums.length; i++) {
      nums[i] = 0;
   }
}

Complexity

Its O(n)

Another Solution (Swapping)

We can do a slight modification to above solution. The point where we just move non-zero value to left. We can do a swap as well.

Code

public void moveZeroes(int[] nums) {
   int left=0;
   
   for (int i=0; i<nums.length; i++) {
      if (nums[i] != 0) {
         //swap
         int t = nums[i];
         nums[i] = nums[left];
         nums[left] = t;
         
         left ++;
      }
   }
}

Complexity

Its O(n)
But, its better since we are not using another loop to copy zero.