Elimination_Game.cpp

class Solution {
    int leftToRight(int n) {
      if(n == 1) return n;
      return 2 * rightToLeft(n / 2);
    }

    int rightToLeft(int n) {
      if(n == 1) return n;
      if(n % 2 == 1) return 2 * leftToRight(n / 2);
      return 2 * leftToRight(n / 2) - 1;
    }
public:
    int lastRemaining(int n) {
        return leftToRight(n);
    }
};