[LeetCode] 189. Rotate Array
阿新 • • 發佈:2018-11-11
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?
題意:一個數組向右“移動”k位
不額外開空間的情況下
這題有個巧妙的演算法,假設k小於length,那麼移動後 就是後k位移到前k位 (假設k為3吧)
1 2 3 4 5 6 7
5 6 7 1 2 3 4(應該得到的結果)
我們把陣列分開,後面的k位和前面的
1 2 3 4 5 6 7
然後各部分翻轉
4 3 2 1 7 6 5
最後一起反轉,就能把後k位翻到前面去
5 6 7 1 2 3 4
class Solution {public void rotate(int[] nums, int k) { if (nums.length == 0 || (k%(nums.length) == 0)) return; int pos = k%nums.length; reverse(nums, 0, nums.length - pos - 1); reverse(nums, nums.length - pos, nums.length - 1); reverse(nums, 0, nums.length - 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--; } } }