leetcode 217:Contains Duplicate

题目：
Given an array of integers, find if the array contains any duplicates. Your function should return true if any value appears at least twice in the array, and it should return false if every element is distinct.
分析：
给定一个数组，判断数组中是否有重复元素。用hashset实现，时间复杂度为O(n).
代码：

public class Solution {    public boolean containsDuplicate(int[] nums) {        if(nums==null || nums.length<2) return false;          Set<Integer> set=new HashSet<Integer>();        for(int i=0; i<nums.length; i++) {              if(set.contains(nums[i])){                return true;            }else{                set.add(nums[i]);            }        }        return false;    }}