189.rotate-array.java

/*
 * @lc app=leetcode id=189 lang=java
 *
 * [189] Rotate Array
 *
 * https://leetcode.com/problems/rotate-array/description/
 *
 * algorithms
 * Easy (28.98%)
 * Total Accepted:    285.4K
 * Total Submissions: 963K
 * Testcase Example:  '[1,2,3,4,5,6,7]\n3'
 *
 * Given an array, rotate the array to the right by k steps, where k is
 * non-negative.
 *
 * Example 1:
 *
 *
 * Input: [1,2,3,4,5,6,7] and k = 3
 * Output: [5,6,7,1,2,3,4]
 * Explanation:
 * rotate 1 steps to the right: [7,1,2,3,4,5,6]
 * rotate 2 steps to the right: [6,7,1,2,3,4,5]
 * rotate 3 steps to the right: [5,6,7,1,2,3,4]
 *
 *
 * Example 2:
 *
 *
 * Input: [-1,-100,3,99] and k = 2
 * Output: [3,99,-1,-100]
 * Explanation:
 * rotate 1 steps to the right: [99,-1,-100,3]
 * rotate 2 steps to the right: [3,99,-1,-100]
 *
 *
 * Note:
 *
 *
 * Try to come up as many solutions as you can, there are at least 3 different
 * ways to solve this problem.
 * Could you do it in-place with O(1) extra space?
 *
 */
class Solution {
  public void rotate(int[] nums, int k) {
    int n = nums.length;
    k = k % n;
    if (k == 0) return;
    reverse(nums, 0, n - k - 1);
    reverse(nums, n - k, n - 1);
    reverse(nums, 0, n - 1);
  }

  public void reverse(int[] nums, int from, int to) {
    while (from < to) {
      int temp = nums[from];
      nums[from++] = nums[to];
      nums[to--] = temp;
    }
  }
}