contains_duplicate.md

217 | Contains Duplicate 👯‍♂️ - Leetcode Day 2

The Challenge: Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

💡 The "Aha!" Moment

Initially, I thought about comparing every number against every other number (Brute Force), but that is too slow for large lists. I realized I didn't need to check everyone against everyone; I just needed a way to remember what I had already seen. If I see a number that is already in my "memory," I know immediately it is a duplicate.

🛠️ My Strategy: The "Bouncer" Set

• Data Structure: I used a Hash Set (seen = set()).
• Mechanism: I treated the Set like a bouncer at a club with a perfect memory.
• Logic: As I iterate through the list, I ask the Set, "Is this number already inside?"
  • Yes: Stop immediately! We found a duplicate. Return True.
  • No: Add the number to the Set and keep moving.

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🐍 Python Implementation

class Solution(object):
    def containsDuplicate(self, nums):
        # Create an empty set to store numbers we have seen
        seen = set()
        
        # Loop through each number in the input array
        for num in nums:
            # Check if the number is already in our set
            if num in seen:
                return True
            
            # If not, add it to the set
            seen.add(num)
            
        # If we finish the loop, no duplicates exist
        return False

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📊 Performance Reflection

Time Complexity: $O(N)$ — We iterate through the list exactly once.

Space Complexity: $O(N)$ — In the worst case (no duplicates), we store every number in the Set.

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✅ Proof of Acceptance :