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+/**%0A * Problem: https://leetcode.com/problems/contains-duplicate/%0A * %0A * 1, Using HashSet to keep the record of every integer which has been visited.%0A * O(n) in computing and space.%0A * %0A * %0A */%0A%0Apublic class Solution %7B%0A    public boolean containsDuplicate(int%5B%5D nums) %7B%0A        HashSet%3CInteger%3E set = new HashSet%3CInteger%3E();%0A        for(int x : nums) %7B%0A            if(set.contains(x)) return true;%0A            set.add(x);%0A        %7D%0A        return false;%0A    %7D%0A%7D%0A

Create Contains_Duplicate.java