Contains Duplicate

class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        numdict = dict()
        for num in nums:
            if num in numdict.keys():
                numdict[num] += 1
            else:
                numdict[num] = 1
        
        for key in numdict.keys():
            if numdict[key] >= 2:
                return True
        
        return False

class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        numset = set()
        for num in nums:
            if num in numset:
                return True
            else:
                numset.add(num)
 
        return False

class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        return len(set(nums)) < len(nums)

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References

https://leetcode.com/problems/contains-duplicate/