Rotate Array

Source

1. leetcode

Rotate an array of n elements to the right by k steps.

For example, with n = 7 and k = 3, the array [1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4].

Note:

Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.

Related Question

1. Rotate String
2. Reverse Words in a String II

Analysis

Can use the algorithm shown in here.

Complexity

Time: O(N)

Space: O(1)

Code

Java

public class Solution {
  public void rotate(int[] nums, int k) {
    if (nums == null || nums.length == 0 || k < 0) {
      return;
    }

    k %= nums.length;
    if (k == 0) {
      return;
    }

    reverse(nums, 0, nums.length - 1);
    reverse(nums, 0, k - 1);
    reverse(nums, k, nums.length - 1);
  }

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

  private void swap(int[] nums, int index1, int index2) {
    int tmp = nums[index1];
    nums[index1] = nums[index2];
    nums[index2] = tmp;
  }
}