Code-Memo

Contains Duplicate

Given an array of integers nums, return True if any value appears at least twice in the array, and return False if every element is distinct.

Example:

nums = [1, 2, 3, 1]
# Output: True (because 1 appears twice)

Solution

class Solution(object):
    def containsDuplicate(self, nums):
        """
        :type nums: List[int]
        :rtype: bool
        """
        nums_set = set()  # Initialize an empty set to store seen numbers
        for num in nums:
            if num in nums_set:
                return True  # If the number is already in the set, return True
            nums_set.add(num)  # Add the number to the set if it's not already there
        return False  # If no duplicates are found, return False

Explanation:

• Time Complexity: O(n)
• Space Complexity: O(n)

Steps:

1. Initialization: Create an empty set nums_set to store seen numbers.

2. Iteration: Iterate through each number num in the nums list using a for loop.

3. Check for Duplicates: For each num, check if it already exists in nums_set.
   • If num is found in nums_set, it means there is a duplicate in the original list nums, so return True.

4. Add to Set: If num is not found in nums_set, add it to the set using nums_set.add(num).

5. Return Default: If the loop completes without finding any duplicates, return False.