The Two Sneaky Numbers of Digitville

Problem Description

Welcome to the whimsical world of Digitville, where numbers are sneaky little creatures that like to hide in plain sight! The problem at hand is to find those elusive numbers that appear exactly twice in a given list. Imagine you’re at a party, and you’re trying to find that one friend who keeps disappearing and reappearing—only this time, it’s numbers playing hide and seek!

In simpler terms, given a list of integers, your task is to identify which numbers appear exactly two times. It’s like trying to find the only two people at a party who are wearing the same outfit—good luck with that!

Code Solution


class Solution:
    def getSneakyNumbers(self, nums: list[int]) -> list[int]:
        return [num for num, freq in collections.Counter(nums).items() if freq == 2]

Approach

The approach here is as straightforward as it gets. We utilize Python’s collections.Counter to count the frequency of each number in the list. Then, we filter out the numbers that appear exactly twice. It’s like having a bouncer at the party who only lets in the guests that RSVP’d twice!

Time and Space Complexity

Time Complexity

O(n), where n is the number of elements in the input list. We traverse the list once to count the frequencies and then again to filter the results.

Space Complexity

O(n) in the worst case, as we may need to store all unique numbers in the list.

Real-World Example

Imagine you’re at a family reunion, and everyone is wearing name tags. You notice that two people are wearing the same name tag—let’s say “Bob.” In this scenario, “Bob” is the sneaky number that appears twice. Just like in our problem, you’re tasked with identifying those name tags that are duplicated.