remove-element.md

Code

func removeElement(nums []int, val int) int {
	i := 0
	for j := 0; j < len(nums); j++ {
		if nums[j] != val {
			nums[i] = nums[j]
			i++
		}
	}
	return i
}

Solution in mind

Intuition

Since this question is asking us to remove all elements of the given value in-place, we have to handle it with O(1) extra space. How to solve it? We can keep two pointers i and j, where iii is the slow-runner while j is the fast-runner.

Algorithm

When nums[j] equals to the given value, skip this element by incrementing j. As long as nums[j] != val, we copy nums[j] to nums[i] and increment both indexes at the same time. Repeat the process until j reaches the end of the array and the new length is i.