# 0217. Contains Duplicate

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

## Description

Given an integer array `nums`, return `true` if any value appears **at least twice** in the array, and return `false` if every element is distinct.

**Example 1:**

```
**Input:** nums = [1,2,3,1]
**Output:** true
```

**Example 2:**

```
**Input:** nums = [1,2,3,4]
**Output:** false
```

**Example 3:**

```
**Input:** nums = [1,1,1,3,3,4,3,2,4,2]
**Output:** true
```

**Constraints:**

* `1 <= nums.length <= 105`
* `-109 <= nums[i] <= 109`

## ac1: set

```java
class Solution {
    public boolean containsDuplicate(int[] nums) {
        // edge case
        if (nums == null || nums.length <= 1) return false;

        Set<Integer> set = new HashSet<>();
        for (int n : nums) {
            if (set.contains(n)) return true;
            set.add(n);
        }

        return false;
    }
}
```

## ac2: sorting

```java
class Solution {
    public boolean containsDuplicate(int[] nums) {
        // edge case
        if (nums == null || nums.length <= 1) return false;

        Arrays.sort(nums);
        for (int i = 1; i < nums.length; i++) {
            if (nums[i] == nums[i-1]) return true;
        }

        return false;
    }
}
```
