674. Longest Continuous Increasing Subsequence


Given an unsorted array of integers, find the length of longest continuous increasing subsequence (subarray).

Example 1:

Input: [1,3,5,4,7]
Output: 3
Explanation: The longest continuous increasing subsequence is [1,3,5], its length is 3. 
Even though [1,3,5,7] is also an increasing subsequence, it's not a continuous one where 5 and 7 are separated by 4.

Example 2:

Input: [2,2,2,2,2]
Output: 1
Explanation: The longest continuous increasing subsequence is [2], its length is 1.

Note: Length of the array will not exceed 10,000.


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Approach #1: Sliding Window [Accepted]

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Intuition and Algorithm

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Every (continuous) increasing subsequence is disjoint, and the boundary of each such subsequence occurs whenever nums[i-1] >= nums[i]. When it does, it marks the start of a new increasing subsequence at nums[i], and we store such i in the variable anchor.

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For example, if nums = [7, 8, 9, 1, 2, 3], then anchor starts at 0 (nums[anchor] = 7) and gets set again to anchor = 3 (nums[anchor] = 1). Regardless of the value of anchor, we record a candidate answer of i - anchor + 1, the length of the subarray nums[anchor], nums[anchor+1], ..., nums[i]; and our answer gets updated appropriately.

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Complexity Analysis

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    Time Complexity: , where is the length of nums. We perform one loop through nums.

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    Space Complexity: , the space used by anchor and ans.

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Analysis written by: @awice.

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