LeetCode ---189. Rotate Array
阿新 • • 發佈:2018-12-05
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Rotate Array題目:
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?
解題思路:題目是對一陣列中的最後一個元素從尾部向頭部進行移動,後面k個元素往前移動和前面n-k個元素進行拼接。
def Solution(array, k): if len(array) == 0 or array is None: return array if k<=len(array): return array[-k:] + array[:-k] if k>len(array): k = k % len(array) return array[-k:] + array[:-k]
Solution
中給到了最優解法(時間複雜度O(n),空間複雜度O(1)), 具體解法見:
解法
第三種解法沒看懂,第四種解法可以參考:
Original List : 1 2 3 4 5 6 7
After reversing all numbers : 7 6 5 4 3 2 1
After reversing first k numbers : 5 6 7 4 3 2 1
After revering last n-k numbers : 5 6 7 1 2 3 4 --> Result
java
public 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--;
}
}
}
Complexity Analysis
Time complexity : O(n). nnn elements are reversed a total of three times.
Space complexity : O(1). No extra space is used.
Ref:
1、https://leetcode.com/problems/rotate-array/description/