Is The Two Sneaky Numbers of Digitville easy or hard?

The problem is classified as Easy. It mainly tests basic array traversal and duplicate detection using a hash table. Candidates familiar with frequency counting patterns can usually solve it quickly in O(n) time.

The Two Sneaky Numbers of Digitville Python/Java solution

In Python, a dictionary or collections.Counter can track frequencies while iterating through the array. In Java, a HashMap performs the same role. Both implementations scan the array once and record values that appear twice.

How to solve The Two Sneaky Numbers of Digitville in O(n)?

Use a frequency dictionary. Iterate through the array and track how many times each value appears. Whenever the count becomes two, add that number to the result list. Because the array is scanned only once and hash lookups are constant time, the total complexity is O(n).

What is the best approach for The Two Sneaky Numbers of Digitville?

The hash table frequency approach is the most efficient and commonly expected solution. Scan the array once while storing counts in a dictionary. When a value reaches frequency two, record it as a sneaky number. This method runs in O(n) time with O(n) extra space.

Is The Two Sneaky Numbers of Digitville asked at Google/Amazon/Meta?

Problems involving duplicate detection and frequency counting are common in interviews at companies like Amazon, Google, and Meta. While the exact problem title may vary, the pattern of identifying repeated numbers in an array using hashing appears frequently in coding rounds.

What data structure is used in The Two Sneaky Numbers of Digitville?

The primary data structure used in the optimal solution is a hash table (dictionary). It stores each number as a key and tracks how many times it appears. Sorting-based solutions instead rely on array ordering and adjacent comparisons.

What is the time complexity of The Two Sneaky Numbers of Digitville?

The optimal hash table solution runs in O(n) time because each element is processed once and dictionary lookups are O(1) on average. A sorting-based approach takes O(n log n) time due to the sorting step followed by a linear scan.

Description Hints 1 Solution Video 27:34

3289. The Two Sneaky Numbers of Digitville

Easy89.9% acceptance4 companies

In the town of Digitville, there was a list of numbers called nums containing integers from 0 to n - 1. Each number was supposed to appear exactly once in the list, however, two mischievous numbers sneaked in an additional time, making the list longer than usual.

As the town detective, your task is to find these two sneaky numbers. Return an array of size two containing the two numbers (in any order), so peace can return to Digitville.

Example 1:

Input: nums = [0,1,1,0]

Output: [0,1]

Explanation:

The numbers 0 and 1 each appear twice in the array.

Example 2:

Input: nums = [0,3,2,1,3,2]

Output: [2,3]

Explanation:

The numbers 2 and 3 each appear twice in the array.

Example 3:

Input: nums = [7,1,5,4,3,4,6,0,9,5,8,2]

Output: [4,5]

Explanation:

The numbers 4 and 5 each appear twice in the array.

Constraints:

2 <= n <= 100
nums.length == n + 2
0 <= nums[i] < n
The input is generated such that nums contains exactly two repeated elements.

Asked at 4 companies

Google Amazon Microsoft Meta

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Hint 1

To solve the problem without the extra space, we need to think about how many times each number occurs in relation to the index.

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3289. The Two Sneaky Numbers of Digitville

Asked at 4 companies

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