LeetCode Challenge Day 46 — 3289. Get Sneaky Numbers

Hey folks 👋

This is Day 46 of my LeetCode streak 🚀
Today’s problem is 3289. Get Sneaky Numbers — an easy array problem that involves finding two numbers that appear twice in the given array.

📌 Problem Statement

You are given an integer array nums of length n + 2 where every integer between 0 and n - 1 appears exactly once, except for two numbers that appear twice.

Return an array containing the two duplicated numbers.

Example 1:

Input: nums = [0, 1, 2, 3, 2, 5, 4, 5]  
Output: [2, 5]

Example 2:

Input: nums = [0, 1, 2, 3, 0, 4, 5, 6]  
Output: [0, 3]

💡 Intuition

Since all numbers except two are unique,
we just need to detect which numbers appear twice.

A simple and efficient way to do this is to use a seen array or set — mark each number the first time it appears, and if it appears again, add it to the result.

🔑 Approach

1. Initialize a boolean array seen of size n to track visited numbers.
2. Iterate through each element in nums.
   • If a number is already marked in seen, it’s a duplicate → add to result.
   • Otherwise, mark it as seen.
3. Stop once both duplicates are found.

⏱️ Complexity Analysis

• Time complexity:
  (O(n)) → Single pass through the array.

• Space complexity:
  (O(n)) → Extra space for the seen array.

🧑‍💻 Code (JavaScript)

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var getSneakyNumbers = function(nums) {
    const n = nums.length - 2;     // since two numbers are duplicated
    const seen = new Array(n).fill(false);
    const res = [];

    for (let num of nums) {
        if (seen[num]) {
            res.push(num);
            if (res.length === 2) break; // found both sneaky numbers
        } else {
            seen[num] = true;
        }
    }

    return res;
};

🧪 Example Walkthrough

Input:
nums = [0, 1, 2, 3, 2, 5, 4, 5]

Steps:

• Seen = []

• 0 → mark seen

• 1 → mark seen

• 2 → mark seen

• 3 → mark seen

• 2 → already seen → add to result

• 5 → mark seen

• 4 → mark seen

• 5 → already seen → add to result

✅ Output = [2, 5]

🎯 Reflection

A nice warm-up problem to strengthen your array manipulation and hashing intuition.
Simple yet satisfying — a perfect reminder that clean thinking leads to clean code ✨

That’s it for Day 46 of my LeetCode journey!
See you tomorrow for Day 47 🔥

Happy Coding 👨‍💻