Leetcode

Rotate Array

  • Time:O(n)
  • Space:O(1)

C++

class Solution {
 public:
  void rotate(vector<int>& nums, int k) {
    k %= nums.size();
    reverse(nums, 0, nums.size() - 1);
    reverse(nums, 0, k - 1);
    reverse(nums, k, nums.size() - 1);
  }

 private:
  void reverse(vector<int>& nums, int l, int r) {
    while (l < r)
      swap(nums[l++], nums[r--]);
  }
};

JAVA

class Solution {
  public void rotate(int[] nums, int k) {
    k %= nums.length;
    reverse(nums, 0, nums.length - 1);
    reverse(nums, 0, k - 1);
    reverse(nums, k, nums.length - 1);
  }

  private void reverse(int[] nums, int l, int r) {
    while (l < r)
      swap(nums, l++, r--);
  }

  private void swap(int[] nums, int l, int r) {
    final int temp = nums[l];
    nums[l] = nums[r];
    nums[r] = temp;
  }
}

Python

class Solution:
  def rotate(self, nums: List[int], k: int) -> None:
    k %= len(nums)
    self.reverse(nums, 0, len(nums) - 1)
    self.reverse(nums, 0, k - 1)
    self.reverse(nums, k, len(nums) - 1)

  def reverse(self, nums: List[int], l: int, r: int) -> None:
    while l < r:
      nums[l], nums[r] = nums[r], nums[l]
      l += 1
      r -= 1