268. Missing Number

https://leetcode.com/problems/missing-number/

Python

Hash Map and remove

class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        possibles = set(range(len(nums)+1))

        for num in nums:
            possibles.remove(num)

        return possibles.pop()

Linear solution from total

class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        n = len(nums)
        total = (n*(n+1))//2
        
        for num in nums:
            total -= num
        
        return total

Javascript

var missingNumber = function(nums) {
   let sum = 0;
    for (let i in nums) {
        sum += nums[i];
    }
    let n = nums.length;
    let sumN = Math.floor((n * (n + 1)) / 2);
  
    return sumN - sum;
};