# Problem Source: LeetCode
# Given an array containing n distinct numbers taken 
# from 0, 1, 2, ..., n, find the one that is missing from the array.

# For example,
# Given nums = [0, 1, 3] return 2.

# Note:
# Your algorithm should run in linear runtime complexity. 
# Could you implement it using only constant extra space complexity?

### ### ###
class Solution(object):
    def missingNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """ 
        n = len(nums)
        s = (n*(n+1))/2
        for i in range(0, len(nums), 1):
            s -= nums[i]
        return s