189. Rotate Array

原题

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].

Could you do it in-place with O(1) extra space?

代码实现

空间复杂度O(1)，时间复杂度O(logn)

    /// <summary>    /// RotateArraySln    /// </summary>    public class RotateArraySln    {        public void Rotate(int[] nums, int k)        {            int n = nums.Length;            if (n == 0 || n == 1) return;            if ((double)k / n > 1)                k = k % n;            if (k == 0) return;            Reverse(nums, 0, n - k); //index, length            Reverse(nums, n - k, k);            Reverse(nums, 0, n);        }        private void Reverse(int[] nums, int index, int length)        {            int i = 0;            int loop = length/2;            while (i < loop)            {                swap(ref nums[index + i], ref nums[length + index - i - 1]);                i++;            }        }        private void swap(ref int a, ref int b)        {            int tmp = a;            a = b;            b = tmp;        }    }

.NET简介版

        public void Rotate(int[] nums, int k)        {            int n = nums.Length;            if (n == 0 || n == 1) return;            if ((double)k / n > 1)                k = k % n;            if (k == 0) return;            System.Array.Reverse(nums, 0, n - k); //index, length            System.Array.Reverse(nums, n - k, k);            System.Array.Reverse(nums);        }