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Find the Longest Valid Obstacle Course at Each Position solution leetcode

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You want to build some obstacle courses. You are given a 0indexed integer array obstacles
of length n
, where obstacles[i]
describes the height of the i^{th}
obstacle.
For every index i
between 0
and n  1
(inclusive), find the length of the longest obstacle course in obstacles
such that:
 You choose any number of obstacles between
0
andi
inclusive.  You must include the
i^{th}
obstacle in the course.  You must put the chosen obstacles in the same order as they appear in
obstacles
.  Every obstacle (except the first) is taller than or the same height as the obstacle immediately before it.
Return an array ans
of length n
, where ans[i]
is the length of the longest obstacle course for index i
as described above.
Example 1:
Input: obstacles = [1,2,3,2] Output: [1,2,3,3] Explanation: The longest valid obstacle course at each position is:  i = 0: [1], [1] has length 1.  i = 1: [1,2], [1,2] has length 2.  i = 2: [1,2,3], [1,2,3] has length 3.  i = 3: [1,2,3,2], [1,2,2] has length 3.
Example 2:
Input: obstacles = [2,2,1] Output: [1,2,1] Explanation: The longest valid obstacle course at each position is:  i = 0: [2], [2] has length 1.  i = 1: [2,2], [2,2] has length 2.  i = 2: [2,2,1], [1] has length 1.
Example 3:
Input: obstacles = [3,1,5,6,4,2] Output: [1,1,2,3,2,2] Explanation: The longest valid obstacle course at each position is:  i = 0: [3], [3] has length 1.  i = 1: [3,1], [1] has length 1.  i = 2: [3,1,5], [3,5] has length 2. [1,5] is also valid.  i = 3: [3,1,5,6], [3,5,6] has length 3. [1,5,6] is also valid.  i = 4: [3,1,5,6,4], [3,4] has length 2. [1,4] is also valid.  i = 5: [3,1,5,6,4,2], [1,2] has length 2.
Constraints:
n == obstacles.length
1 <= n <= 10^{5}
1 <= obstacles[i] <= 10^{7}

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