Grokking the Coding Interview: Patterns for Coding Questions

Problem Challenge 3: Employee Free Time (hard) 

## Problem Statement

For ‘K’ employees, we are given a list of intervals representing each employee’s working hours. Our goal is to determine if there is a **free interval which is common to all employees**. 

**Example 1**:
```
Input: Employee Working Hours=[[[1,3], [5,6]], [[2,3], [6,8]]]
Output: [3,5]
Explanation: All the employees are free between [3,5].
```
**Example 2**:
```
Input: Employee Working Hours=[[[1,3], [9,12]], [[2,4]], [[6,8]]]
Output: [4,6], [8,9]
Explanation: All employees are free between [4,6] and [8,9].
```
**Example 3**:
```