# 3. Contains Duplicate

{% embed url="<https://leetcode.com/problems/contains-duplicate/>" %}

```javascript

    const map = {};
    for (const num of nums) {
        if (map[num] === 1) return true;
        map[num] = 1;
    }

    return false
```

```javascript
var containsDuplicate = function(nums) {    
    return new Set(nums).size !== nums.length;
}; 
```