Move Zeros

Problem

Given an integer array nums, move all zeros to the end while keeping the relative order of the non-zero elements. Do it in-place.

Constraints

• 1 ≤ nums.length ≤ 10⁴
• −2³¹ ≤ nums[i] ≤ 2³¹ − 1

Approach — Two Pointers

This is a Two Pointers problem. The idea: walk two indices through the data together (or toward each other), turning an O(n²) pair search into one linear pass. Work through the reference code below line by line, then re-derive it yourself in the editor — that's how the pattern sticks.

Complexity: O(n) time, O(1) extra space.

Solution code

Python

class Solution:
    def moveZeroes(self, nums):
        j = 0
        for i in range(len(nums)):
            if nums[i] != 0:
                nums[j], nums[i] = nums[i], nums[j]
                j += 1
        return nums

Java

class Solution {
    public void moveZeroes(int[] nums) {
        int write = 0;
        // First pass: write every non-zero compactly from the front.
        for (int num : nums) {
            if (num != 0) {
                nums[write++] = num;
            }
        }
        // Second pass: fill the rest with zeros.
        while (write < nums.length) {
            nums[write++] = 0;
        }
    }
}

Practice it

Reading a solution isn't the same as being able to write it under pressure. Open this problem in the in-browser editor, hide the solution, and solve it from scratch — your code runs against real test cases instantly.