To modify the array so that all zeros are moved to the end while maintaining the order of non-zero elements [closed]

Question

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

My Solution:-

public class MoveZeros {
    public void moveZeroes(int[] nums) {

        List<Integer> li = new ArrayList<Integer>(nums.length);
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] != 0) {
                li.add(nums[i]);
            }
        }
        while (nums.length > li.size()) {
            li.add(0);
        }
        for (int i = 0; i < li.size(); i++)
            nums[i] = li.get(i);
    }

    public static void main(String[] args) {
        int num[] = { 0, 1, 0, 3, 12 };
        MoveZeros move = new MoveZeros();
        move.moveZeroes(num);
        System.out.println(Arrays.toString(num));
    }
}

Any other way we can solve this problem?

Answer 1

We can do this without moving the zeros:

• We keep track of the number of positions that we have non-zero elements (using if (num != 0)). Simultaneously, we move the non-zero elements to the beginning of the nums array.
• Then, we set all elements after the pos count to zero.

import java.util.Arrays;

public class MoveZeros {
    public static void moveZeroes(int[] nums) {
        if (nums == null || nums.length == 0)
            return;

        int pos = 0;
        for (int num : nums) {
            if (num != 0) {
                nums[pos++] = num;
            }
        }
        while (pos < nums.length) {
            nums[pos++] = 0;
        }
    }

    public static void main(String[] args) {
        int[] nums = { 0, 1, 0, 3, 12 };
        MoveZeros.moveZeroes(nums);
        System.out.println(nums == null ? "null" : Arrays.toString(nums));
    }
}

Prints

[1, 3, 12, 0, 0]

---

Comments:

• BTW, static methods should be invoked using the class name, not via an instance. – WJS

Answer 2

Here is my method for your reference.

If the element i of array is 0, left shift the array and put 0 to the last (calculate --n to avoid checking the 0s again). If the element i of array is not 0, then check the next one, i.e. i + 1.

public class MoveZeros {
    public void moveZeroes(int[] nums) {
        int i = 0, n = nums.length;
        while(i < n)
            if (nums[i] == 0) {
                for (int j = i + 1; j < n; j++)
                    nums[j - 1] = nums[j];
                nums[--n] = 0;
            } else {
                i++;
            }
    }
    
    public static void main(String[] args) {
        int num[] = { 0, 1, 0, 3, 12 };
        MoveZeros move = new MoveZeros();
        move.moveZeroes(num);
        System.out.println(Arrays.toString(num));
    }
}