Time:O(\log n) Space:O(\log n) C++ class Solution { public: int lastRemaining(int n) { return n == 1 ? 1 : 2 * (1 + n / 2 - lastRemaining(n / 2)); } }; JAVA class Solution { public int lastRemaining(int n) { return n == 1 ? 1 : 2 * (1 + n / 2 - lastRemaining(n / 2)); } }