Leetcode grind

remove-element.py

class Solution:
    def removeElement(self, nums: List[int], val: int) -> int:
        '''
        while right pointer > left pointer

        - check through from the right pointer
        - move cursor to the left if the number there equals target
        - else check through from the left pointer
            - if number equals target, swap the left with the right
                - move the left forward
            - else move the left forward 

        2

        [0,1,2,2,2,2,4,2]
                 l
                     r

        [2, 2, 3, 3]

            l
            r
        '''

        if len(nums) == 0:
            return 0

        count, l = 0, 0
        
        for r in range(len(nums)):
            if nums[r] != val:
                nums[l] = nums[r]
                l += 1
            else:
                count += 1

        return len(nums) - count

two-sum.py

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        # trivial solution
        '''
        for i in range(len(nums)):
            for j in range(i+1, len(nums)):
                if nums[i] + nums[j] == target:
                    return [i, j]
        '''

        # efficient solution
        hashmap = dict()

        for i in range(len(nums)):
            othernum = target - nums[i]

            if othernum in hashmap:
                return [i, hashmap[othernum]]
            else:
                hashmap[nums[i]] = i