[LeetCode] 581. Shortest Unsorted Continuous Subarray

轉自LeetCode

Given an integer array, you need to find one continuous subarray that if you only sort this subarray in ascending order, then the whole array will be sorted in ascending order, too.

You need to find the shortest such subarray and output its length.

Example 1:

Input: [2, 6, 4, 8, 10, 9, 15]
Output: 5
Explanation: You need to sort [6, 4, 8, 10, 9] in ascending order to make the whole array sorted in ascending order.

Note:

1. Then length of the input array is in range [1, 10,000].
2. The input array may contain duplicates, so ascending order here means <=.

<Solution>

想法如下

• 用一個 stack 來存放目前已經檢查過的 index

• 先從 array 的頭開始找，正常來說值應該是愈來愈大，所以如果發現值變小了，就在 stack 裡找到這個值，應該在的位置

• 同理，從 array 的尾往前找，正常來說值應該是愈來愈小，所以如果發現值變大了，就在 stack 裡找到這個值，應該在的位置

• 經過上面兩步驟後，就可以找出 subarray 的左邊界和右邊界

Code 如下

Java