217. Contains Duplicate

https://leetcode.com/problems/contains-duplicate/description/
解题思路：
用hashset来解决

class Solution {
public boolean containsDuplicate(int[] nums) {

    if(nums == null) return false;
    Set<Integer> set = new HashSet<Integer>();
    for(int i = 0; i < nums.length; i++){
        if(set.contains(nums[i]))
            return true;
        set.add(nums[i]);
    }
    return false;
}

}