#283 - Move Zeroes

EasyTwo Pointers

Given an integer array nums, move all 0's to the end while maintaining the relative order of the non-zero elements. You must do this in-place without making a copy of the array.

Input	Output
nums = [0,1,0,3,12]	[1,3,12,0,0]
nums = [0]	[0]
nums = [1,2,3]	[1,2,3]

Solution Space

Try it

/**
 * Moves all zeros to the end of the array in-place,
 * preserving the relative order of non-zero elements.
 *
 * @param nums Array of integers (modified in-place)
 */
export function moveZeroes(nums: number[]): void {
  let writeIdx = 0;

  for (let readIdx = 0; readIdx < nums.length; readIdx++) {
    if (nums[readIdx] !== 0) {
      // Swap keeps non-zeros in order and pushes zeros right
      [nums[writeIdx], nums[readIdx]] = [nums[readIdx], nums[writeIdx]];
      writeIdx++;
    }
  }
}

Approach: two-pointer (read/write) – use a read pointer to scan the array and a write pointer to place non-zero elements, then fill the rest with zeros.

Time: O(n) – single pass through the array.

Space: O(1) – in-place swaps, no extra storage.

Alternative approaches:

Approach	Idea	Time	Space
Two-pass overwrite	First pass: copy all non-zeros to the front. Second pass: fill the rest with zeros.	O(n)	O(1)

Why the swap approach is preferred:

• Single pass instead of two, and naturally preserves the relative order with minimal writes.

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