Lintcode Recover Rotated Sorted Array

Given a rotated sorted array, recover it to sorted array in-place.

Example

[4, 5, 1, 2, 3] -> [1, 2, 3, 4, 5]

Challenge

In-place, O(1) extra space and O(n) time.

Clarification

What is rotated array?

For example, the orginal array is [1,2,3,4], The rotated array of it can be [1,2,3,4], [2,3,4,1], [3,4,1,2], [4,1,2,3]

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解题思路：

技巧题：知道就知道题，不知道就拉倒题。

找到分割位置，什么时候出现下降就是分割位置。

三步翻转法：

1. [1,2,3]翻转一下变成[3,2,1]
2. [4,5]翻转变成[5,4]

3. 最后全部翻转一下就得到。

相关类似题目：

1. Rotate String: abcdefg, offset = 3 -> efgabcd

方法：三步翻转法：

    (1) adcd efg

    (2) dcda gfe

    (3) efgabcd

1. Rotate Words List: I love you -> you love I

方法：二步翻转法：

  (1)全部翻转

  (2)根据空格每个单词翻转

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Java code:

public class Solution {
    /**
     * @param nums: The rotated sorted array
     * @return: void
     */
    public void recoverRotatedSortedArray(ArrayList<Integer> nums) {
        // write your code
        for(int i = 0; i < nums.size() - 1 ; i++) {
            if(nums.get(i) > nums.get(i+1)) {
                reverse(nums, 0, i);
                reverse(nums, i+1, nums.size()-1);
                reverse(nums, 0 , nums.size()-1);
                return;
            }
        }
        
    }
    public void reverse(ArrayList<Integer> nums, int start, int end) {
        for(int i = start, j = end; i< j; i++, j--) {
            int temp = nums.get(i);
            nums.set(i, nums.get(j));
            nums.set(j, temp);
        }
    }
}

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Reference:

1. http://www.jiuzhang.com/solutions/recover-rotated-sorted-array/