27_Remove Element

Given an array nums and a value val, remove all instances of that value in-place and return the new length.

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

The order of elements can be changed. It doesn't matter what you leave beyond the new length.

Example:

Given nums = [3,2,2,3], val = 3,
Your function should return length = 2, with the first two elements of nums being 2.
It doesn't matter what you leave beyond the returned length.

Solution:

def removeElement(nums, val):
    """
    :type nums: List[int]
    :type val: int
    :rtype: int
    """
    # corner cases
    if len(nums) == 0:
        return 0

    write_index = 0
    for i in range(len(nums)):
        if nums[i] != val:
            nums[write_index], nums[i] = nums[i], nums[write_index]
            write_index += 1
    return write_index