Description
You have a list arr of all integers in the range [1, n] sorted in a strictly increasing order. Apply the following algorithm on arr:
- Starting from left to right, remove the first number and every other number afterward until you reach the end of the list.
- Repeat the previous step again, but this time from right to left, remove the rightmost number and every other number from the remaining numbers.
- Keep repeating the steps again, alternating left to right and right to left, until a single number remains.
Given the integer n, return the last number that remains in arr.
Example 1:
Input: n = 9 Output: 6 Explanation: arr = [1, 2, 3, 4, 5, 6, 7, 8, 9] arr = [2, 4, 6, 8] arr = [2, 6] arr = [6]
Example 2:
Input: n = 1 Output: 1
Constraints:
1 <= n <= 109
Solutions
Solution 1
PythonJavaC++Go
class Solution: def lastRemaining(self, n: int) -> int: a1, an = 1, n i, step, cnt = 0, 1, n while cnt > 1: if i % 2: an -= step if cnt % 2: a1 += step else: a1 += step if cnt % 2: an -= step cnt >>= 1 step <<= 1 i += 1 return a1(code-box)
