189. Rotate Array

Given an array, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: nums = [1,2,3,4,5,6,7], 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: nums = [-1,-100,3,99], 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]

三次反轉。

TC: O(n), SC: O(1)

public class Solution {
    public void rotate(int[] nums, int k) {
        k %= nums.length; // [1,2,3,4,5,6,7]
        reverse(nums, 0, nums.length - 1); // [7,6,5,4,3,2,1]
        reverse(nums, 0, k - 1); //[5,6,7,4,3,2,1]
        reverse(nums, k, nums.length - 1); // [5,6,7,1,2,3,4]
    }

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

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