Move Zeroes in Java (Stable In-Place)

Move Zeroes in Java (Stable In-Place)

This guide explains the intuition, optimized approach, and Java implementation for move zeroes in java (stable in-place), with practical tips for interviews and production coding standards.

Problem

Move all 0s to end while preserving non-zero order.

Approach

Use write index insertPos for next non-zero value.

1. Copy non-zero values forward.
2. Fill remaining positions with zero.

Java Solution

class Solution {
    public void moveZeroes(int[] nums) {
        int insertPos = 0;

        for (int n : nums) {
            if (n != 0) {
                nums[insertPos++] = n;
            }
        }

        while (insertPos < nums.length) {
            nums[insertPos++] = 0;
        }
    }
}

Complexity

• Time: O(n)
• Space: O(1)

Key Takeaways

• Start from the brute-force idea, then derive the optimized invariant.
• Use clean pointer/index boundaries to avoid off-by-one bugs.
• Validate against edge cases (empty input, single element, duplicates, extreme values).