The Number of the Smallest Unoccupied Chair

There is a party where `n` friends numbered from `0` to `n - 1` are attending. There is an **infinite** number of chairs in this party that are numbered from `0` to `infinity`. When a friend arrives at the party, they sit on the unoccupied chair with the **smallest number**. - For example, if chairs `0`, `1`, and `5` are occupied when a friend comes, they will sit on chair number `2`. When a friend leaves the party, their chair becomes unoccupied at the moment they leave. If another friend arrives at that same moment, they can sit in that chair. You are given a **0-indexed** 2D integer array `times` where `times[i] = [arrivali, leavingi]`, indicating the arrival and leaving times of the `ith` friend respectively, and an integer `targetFriend`. All arrival times are **distinct**. Return_ the **chair number** that the friend numbered _`targetFriend`_ will sit on_.   **Example 1:** **Input:** times = [[1,4],[2,3],[4,6]], targetFriend = 1 **Output:** 1 **Explanation:** - Friend 0 arrives at time 1 and sits on chair 0. - Friend 1 arrives at time 2 and sits on chair 1. - Friend 1 leaves at time 3 and chair 1 becomes empty. - Friend 0 leaves at time 4 and chair 0 becomes empty. - Friend 2 arrives at time 4 and sits on chair 0. Since friend 1 sat on chair 1, we return 1. ``` **Example 2:** **Input:** times = [[3,10],[1,5],[2,6]], targetFriend = 0 **Output:** 2 **Explanation:** - Friend 1 arrives at time 1 and sits on chair 0. - Friend 2 arrives at time 2 and sits on chair 1. - Friend 0 arrives at time 3 and sits on chair 2. - Friend 1 leaves at time 5 and chair 0 becomes empty. - Friend 2 leaves at time 6 and chair 1 becomes empty. - Friend 0 leaves at time 10 and chair 2 becomes empty. Since friend 0 sat on chair 2, we return 2. ```   **Constraints:** - `n == times.length` - `2 <= n <= 104` - `times[i].length == 2` - `1 <= arrivali < leavingi <= 105` - `0 <= targetFriend <= n - 1` - Each `arrivali` time is **distinct**.