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]
.
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?
Related problem: Reverse Words in a String II
解题思路:
要想满足O(1) space and in O(n) time, 只有一种方法: 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
或者
(1) reverse the array;
(2) reverse the first k elements;
(3) reverse the last n-k elements.
这个方法与 Leetcode Reverse Words in a String II 达成一致。
Java code:
public class Solution { public void rotate(int[] nums, int k) { int len = nums.length; k %= len; reverse(nums, 0, len-1); reverse(nums, 0, k-1); reverse(nums, k, len-1); } public void reverse(int[] nums, int l, int r){ while(l < r){ int temp = nums[l]; nums[l] = nums[r]; nums[r] = temp; l++; r--; } } }
Reference:
1. http://www.cnblogs.com/EdwardLiu/p/4306556.html