Solution 1Hash Set

class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        prev = set()
        for n in nums:
            if n in prev:
                return True
            prev.add(n)
        return False
Leet Code/python.py · L70–78
public boolean containsDuplicate(int[] nums) {
    Set<Integer> prevNums = new HashSet<Integer>();
    for(int num: nums) {
        if(prevNums.contains(num)) {
            return true;
        }
        prevNums.add(num);
    }
    return false;
}
Leet Code/java.java · L5–15

Solution 2Set Length

Python
class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        return len(nums) != len(set(nums))
Leet Code/python.py · L79–82