You are given an array of positive integers and a number k. In one operation, you remove the last element of the array. The goal is to find the minimum number of operations required to collect all numbers from 1 to k at least once.
This Easy-level problem is used by firms like Deutsche Bank to assess basic coding speed and correct use of set data structures. It tests if a candidate can iterate through an array efficiently (from the end) and use a hash set to track a collection of required items.
The pattern is Array Traversal (Backward) and Hash Table (Set). You iterate from the end of the array towards the beginning. For each element, if it is less than or equal to k, you add it to a set. Once the size of the set reaches k, you stop and return the number of elements removed.
Array: [3, 1, 5, 4, 2], k: 2.
A common error is iterating from the front, which is much less efficient because you don't know when you've "collected" the final required element until you reach the end. Some candidates also forget to check the condition element <= k before adding to the set, which might fill the set with irrelevant numbers.
Always pay attention to whether "collecting" starts from a specific side of a data structure. In this case, "removing the last element" is a clear signal to process the array in reverse.
| Title | Difficulty | Topics | LeetCode |
|---|---|---|---|
| Find the XOR of Numbers Which Appear Twice | Easy | Solve | |
| Two Out of Three | Easy | Solve | |
| Count Pairs of Points With Distance k | Medium | Solve | |
| Find the Prefix Common Array of Two Arrays | Medium | Solve | |
| Triples with Bitwise AND Equal To Zero | Hard | Solve |
