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Contains Duplicate

Return true if any value appears at least twice in the array.

Answers use simple, clear English.

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Quick interview answer

Insert into a set while iterating; if an element is already present, return true. O(n) time, O(n) space. Sorting is O(n log n) with O(1) extra if allowed to mutate.

Detailed answer

Insert into a set while iterating; if an element is already present, return true. O(n) time, O(n) space. Sorting is O(n log n) with O(1) extra if allowed to mutate.

Code example

def contains_duplicate(nums: list[int]) -> bool:
    seen = set()
    for x in nums:
        if x in seen: return True
        seen.add(x)
    return False

Practice code · python (view only · no execution)

def contains_duplicate(nums: list[int]) -> bool:
    seen = set()
    for x in nums:
        if x in seen: return True
        seen.add(x)
    return False

#array#hashset