leetcode-go/leetcode/medium/390.elimination-game.go

func lastRemaining(n int) int {
	// 1 2 3 4 5 6 -> 2 4 6 -> 2 * (1 2 3) -> 2 * (n/2 + 1 - remaining)
	if n == 1 {
		return 1
	}
	return 2 * (n/2 + 1 - lastRemaining(n/2))
}