Source: https://leetcode.com/problems/contains-duplicate/

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.

**Example 1:**

Input:[1,2,3,1]Output:true

**Example 2:**

Input:[1,2,3,4]Output:false

**Example 3:**

Input:[1,1,1,3,3,4,3,2,4,2]Output:true

This problem is super easy. we just traverse the array. And put every number to a HashSet. If we found any new number is in the HashSet already, we know we have duplicate, return true. If in the end we still can’t find a duplicate, we return false.

Github: https://github.com/tinyfool/leetcode/tree/master/src/p0217

To see more hashtable related problems, see

Problems and Solutions of Hashmap.