27. Remove Element

O(n)

class Solution:
    def removeElement(self, nums: List[int], val: int) -> int:
        i = 0
        for x in nums:
            if x != val:
                nums[i] = x
                i += 1
        return i

class Solution {
public:
    int removeElement(vector<int>& nums, int val) {
        int i = 0;
        for (int x : nums) {
            if (x != val) {
                nums[i++] = x;
            }
        }
        return i;
    }
};

class Solution {
public:
    int removeElement(vector<int>& nums, int val) {
        int n = nums.size();
        for (int i = n - 1; i >= 0; --i) {
            if (nums[i] == val) {
                swap(nums[i], nums[--n]);
                nums.pop_back();
            }
        }
        return nums.size();
    }
};