189

189. Rotate Array (Medium)

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]

 

Constraints:

• 1 <= nums.length <= 105
• -231 <= nums[i] <= 231 - 1
• 0 <= k <= 105

 

Follow up:

• Try to come up with as many solutions as you can. There are at least three different ways to solve this problem.
• Could you do it in-place with O(1) extra space?

Companies:
Amazon, Microsoft, Facebook, Google, Adobe, Apple, Yahoo, tcs

Related Topics:
Array, Math, Two Pointers

Similar Questions:

• Rotate List (Medium)
• Reverse Words in a String II (Medium)

Solution 1.

// OJ: https://leetcode.com/problems/rotate-array/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(K)
class Solution {
public:
    void rotate(vector<int>& A, int k) {
        int N = A.size();
        k %= N;
        if (k == 0) return;
        vector<int> tmp(k);
        for (int i = 0; i < k; ++i) tmp[i] = A[N + i - k];
        for (int i = N - k - 1; i >= 0; --i) A[i + k] = A[i];
        for (int i = 0; i < k; ++i) A[i] = tmp[i];
    }
};

Solution 2. In-place Rotation

// OJ: https://leetcode.com/problems/rotate-array/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    void rotate(vector<int>& A, int k) {
        int cnt = 0, N = A.size();
        k %= N;
        if (k == 0) return;
        for (int i = 0; cnt < N; ++i) {
            int j = i, tmp = A[j];
            do {
                int t = (j + k) % N, next = A[t];
                A[t] = tmp;
                tmp = next;
                j = t;
                ++cnt;
            } while (j != i);
        }
    }
};

Solution 3.

// OJ: https://leetcode.com/problems/rotate-array/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    void rotate(vector<int>& A, int k) {
        k = (2 * A.size() - k) % A.size();
        if (k == 0) return;
        reverse(begin(A), begin(A) + k);
        reverse(begin(A) + k, end(A));
        reverse(begin(A), end(A));
    }
};