class Solution(object):
    def lastRemaining(self, n):
        """
        :type n: int
        :rtype: int
        """
        return ((n | 0x55555555555555) & ((1 << (n.bit_length() - 1)) - 1)) + 1

Add py solution for 390. Elimination Game
Add py solution for 390. Elimination Game

390. Elimination Game: https://leetcode.com/problems/elimination-game/

Approach:
    Observe the first item remaining in each step. The value will be added
    1 << step either the remaining count is odd or it's a left-to-right
    step. Hence the n | 0x55555.. is the key.
