#217EasyHash Set

Contains Duplicate

Detect if any value appears at least twice using a hash set.

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Problem Statement

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.

Examples

Example 1

Input:nums = [1,2,3,1]
Output:true

Explanation: 1 appears at index 0 and 3.

Example 2

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

Explanation: All elements are distinct.

Constraints

  • 1 ≤ nums.length ≤ 10⁵
  • -10⁹ ≤ nums[i] ≤ 10⁹

Solutions

1
Brute Force — Nested Loops
TimeO(n²)SpaceO(1)

Compare every pair of elements. If any two are equal, return true. O(n²) time — fine for small inputs but too slow for n=10⁵.

Visual Animation
def containsDuplicate(nums: list[int]) -> bool:
    n = len(nums)
    for i in range(n):
        for j in range(i + 1, n):
            if nums[i] == nums[j]:
                return True
    return False

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