Missing Number

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

Solution 1: Indexing

table = [0] * (len(nums) + 1)
for num in nums:
    table[num] = 1
return table.index(0)

Solution 2: Gauss’s Formula (Summation)

n = len(nums)
return n * (n + 1) // 2 - sum(nums)

Solution 3: XOR

missing = len(nums)
for i, num in enumerate(nums):
    missing ^= i ^ num
return missing

Utilizing the fact that x ^ x = 0, and x ^ 0 = x. The index and number cancels each other. Initialize missing = len(nums), since the index n is not iterated.