21. Find the Most Competitive Subsequence.cpp

/*
Find the Most Competitive Subsequence
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Given an integer array nums and a positive integer k, return the most competitive subsequence of nums of size k.

An array's subsequence is a resulting sequence obtained by erasing some (possibly zero) elements from the array.

We define that a subsequence a is more competitive than a subsequence b (of the same length) if in the first position where a and b differ, subsequence a has a number less than the corresponding number in b. For example, [1,3,4] is more competitive than [1,3,5] because the first position they differ is at the final number, and 4 is less than 5.

Example 1:
Input: nums = [3,5,2,6], k = 2
Output: [2,6]
Explanation: Among the set of every possible subsequence: {[3,5], [3,2], [3,6], [5,2], [5,6], [2,6]}, [2,6] is the most competitive.

Example 2:
Input: nums = [2,4,3,3,5,4,9,6], k = 4
Output: [2,3,3,4]

Constraints:
1 <= nums.length <= 105
0 <= nums[i] <= 109
1 <= k <= nums.length

Hint #1  
In lexicographical order, the elements to the left have higher priority than those that come after. Can you think of a strategy that incrementally builds the answer from left to right?
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