#2501
Longest Square Streak in an Array
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array · hash table · binary search · dynamic programming · sorting
Description
You are given an integer array nums. A subsequence of nums is called a square streak if:
- The length of the subsequence is at least 2, and
- after sorting the subsequence, each element (except the first element) is the square of the previous number.
Return the length of the longest square streak in nums, or return -1 if there is no square streak.
A subsequence is an array that can be derived from another array by deleting some or no elements without changing the order of the remaining elements.
Example 1:
Input: nums = [4,3,6,16,8,2]
Output: 3
Explanation: Choose the subsequence [4,16,2]. After sorting it, it becomes [2,4,16].
- 4 = 2 * 2.
- 16 = 4 * 4.
Therefore, [4,16,2] is a square streak.
It can be shown that every subsequence of length 4 is not a square streak.
Example 2:
Input: nums = [2,3,5,6,7]
Output: -1
Explanation: There is no square streak in nums so return -1.
Solution