Python

1. Two Sum

Was able to do this from one list where, get the compliment and check from i+1 index forward within the list to see if the value exists in there or not

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        for i, num in enumerate(nums):
            compliment = target - num 
            if compliment in nums[i+1:]:
                idx = nums.index(compliment, i+1)
                out = [i, idx]
                return out
        
        return None

20. Valid Parentheses

I created a dictionary with matching brackets and created a stack using collections deque

iterated through the string of brackets and if it was opening I added it to the stack, then if it is closing, I checked the last bracket added to the stack and made sure the closing bracket matched

If it matched, I popped from the deque since it is LIFO

If it didn’t match, then I returned False

And once the stack is empty at the end of the loop I returned True

from collections import deque

class Solution:
    def isValid(self, s: str) -> bool:
        stack = deque()
        opening_brackets = {'[' : ']', '{' : '}', '(' : ')'}

        if len(s) == 1:
            return False

        for bracket in s:
            #check if it is an opening bracket
            if bracket in opening_brackets.keys():
                #add it to the stack
                stack.append(bracket)
            else:
                #check if the top of the stack is the closer to it
                if not stack or opening_brackets[stack[-1]] != bracket:
                    return False
                stack.pop()
        if stack:
            return False 
            
        return True

1. Remove Element

Used list comprehension to remove the element from within the list itself. The [:] specifies that it is does in place

class Solution:
    def removeElement(self, nums: List[int], val: int) -> int:
        #iterate through nums
        nums[:] = [num for num in nums if num != val]
        return len(nums)

1. Search Insert Position