189. Rotate Array(三步旋轉法)
阿新 • • 發佈:2018-12-19
【題目】
Given an array, rotate the array to the right by k steps, where k is non-negative.
(翻譯:給定一個數組,將陣列中的元素向右移動 k 個位置,其中 k 是非負數。)
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]
【分析】
採用經典的三步旋轉法:
- 將整個陣列 (array) 的元素前後顛倒得到array1(即:index: 0 與 index: array.length - 1)
- 將array1的前k個元素前後顛倒得到array2(即:index: 0 與 index: k -1)
- 將array2的後n - k(n為陣列元素個數)個元素前後顛倒得到array3,即最終結果
Java程式碼實現如下:
class Solution { public void rotate(int[] nums, int k) { k %= nums.length; reverse(nums, 0, nums.length - 1); reverse(nums, 0, k - 1); reverse(nums, k, nums.length - 1); } public void reverse(int[] nums, int start, int end) { while (start < end) { int temp = nums[start]; nums[start] = nums[end]; nums[end] = temp; start++; end--; } } }