leetCode_189. Rotate Array (旋轉陣列)
阿新 • • 發佈:2018-12-15
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?
題目解析
思路:1 找到中心點
2.將中心點左邊資料反轉(不包括中心點)
3.將中心點右邊資料反轉(包括中心點)
4. 將反轉後的資料合併
5.合併後的資料反轉即可得到答案
時間複雜度為o(n) 空間複雜度為o(1)
class Solution { public void rotate(int[] nums, int k) { int length = nums.length; k = k%length; if(length==1) return; if(k==0) return; reversal(nums,0,length-k-1); reversal(nums,length-k,length-1); reversal(nums,0,length-1); } public static void reversal(int[] nums,int i,int j){ int t = 0; while (i < j && i >= 0) { t = nums[i]; nums[i] = nums[j]; nums[j] = t; i++; j--; } } }