189. Rotate Array

• Difficulty: Easy

• Topics: Array

• Similar Questions:

  • Rotate List

  • Reverse Words in a String II

Problem:

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?

Solutions:

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

    void swap(vector<int>& nums, int left, int right) {
        while (left < right) {
            int temp = nums[left];
            nums[left] = nums[right];
            nums[right] = temp;
            left++;
            right--;
        }
    }
};