Rotate Array 解答

Question

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].

Solution 1 Bubble Rotate

Similar with bubble sort, time complexity O(k * n), space cost O(1)

 public class Solution {

     public void rotate(int[] nums, int k) {

         int length = nums.length;

         if (k >= length)

             k = k % length;

         if (k == 0)

             return;

         for (int i = 0; i < k; i++) {

             for (int j = length - 1; j > 0; j--) {

                 int tmp = nums[j];

                 nums[j] = nums[j - 1];

                 nums[j - 1] = tmp;

             }

         }

     }

 }

Solution 2 Traverse

Key to this solution is to make a copy of original array. Time complexity O(n), space cost O(n).

Solution 3 Reversal

Assuming we are given {1,2,3,4,5,6} and order 2. The basic idea is:

1. Divide the array two parts: 1,2,3,4 and 5, 6

2. Rotate first part: 4,3,2,1,5,6

3. Rotate second part: 4,3,2,1,6,5

4. Rotate the whole array: 5,6,1,2,3,4

Time complexity O(n), space cost O(n)

 public class Solution {

     public void rotate(int[] nums, int k) {

         int length = nums.length;

         if (k >= length)

             k = k % length;

         if (k == 0)

             return;

         reverse(nums, 0, length - k - 1);

         reverse(nums, length - k, length - 1);

         reverse(nums, 0, length - 1);

     }

     private void reverse(int[] nums, int start, int end) {

         if (start == end || nums.length == 1)

             return;

         while (start < end) {

             int tmp = nums[start];

             nums[start] = nums[end];

             nums[end] = tmp;

             start++;

             end--;

         }

     }

 }

巴特西

Rotate Array 解答

Question

Solution 1 Bubble Rotate

Solution 2 Traverse

Solution 3 Reversal

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