Program to find the most competitive subsequence in Python

Suppose we have an array nums and another value k, we have to find the most competitive subsequence of nums of size k. Here a subsequence s1 is more competitive than a subsequence s2 (of equal size) if in the first position where s1 and s2 differ, subsequence s1 has a number less than the corresponding number in s2.

So, if the input is like nums = [4,6,3,7] k = 2, then the output will be [3,7] because among all subsequences of size 2, {[4,6], [4,3], [4,7], [6,3], [6,7], [3,7]}, the [3,7] is the most competitive.

To solve this, we will follow these steps −

• attempts := size of nums - k
• stack := a new list
• for each num in nums, do
  • while stack is not empty and num < top of stack and attempts > 0, do
    • pop element from stack
    • attempts := attempts - 1
  • push num into stack
• return top k elements of stack

Example

Let us see the following implementation to get better understanding −

def solve(nums, k):
   attempts = len(nums) - k
   stack = []
   for num in nums:
      while stack and num < stack[-1] and attempts > 0:
         stack.pop()
         attempts -= 1
      stack.append(num)

   return stack[:k]

nums = [4,6,3,7]
k = 2
print(solve(nums, k))

Input

[4,6,3,7], 2

Output

[3,7]

Arnab Chakraborty

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Updated on: 05-Oct-2021

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