LeetCode in Kotlin

1942. The Number of the Smallest Unoccupied Chair

Medium

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.

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:

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:

Since friend 0 sat on chair 2, we return 2.

Constraints:

Solution

import java.util.PriorityQueue

class Solution {
    fun smallestChair(times: Array<IntArray>, targetFriend: Int): Int {
        val minheap = PriorityQueue<Int>()
        minheap.offer(0)
        val all = arrayOfNulls<Person>(times.size * 2)
        for (i in times.indices) {
            all[2 * i] = Person(i, times[i][0], false, true)
            all[2 * i + 1] = Person(i, times[i][1], true, false)
        }

        all.sortWith { a: Person?, b: Person? ->
            val i = if (a!!.leave) -1 else 1
            val j = if (b!!.leave) -1 else 1
            if (a.time == b.time) i - j else a.time - b.time
        }
        val seat = IntArray(times.size)
        var i = 0
        while (true) {
            if (all[i]!!.arrive) {
                if (targetFriend == all[i]!!.idx) {
                    return minheap.peek()
                }
                seat[all[i]!!.idx] = minheap.poll()
                if (minheap.isEmpty()) {
                    minheap.offer(seat[all[i]!!.idx] + 1)
                }
            } else {
                minheap.offer(seat[all[i]!!.idx])
            }
            i++
        }
    }

    private class Person internal constructor(var idx: Int, var time: Int, var leave: Boolean, var arrive: Boolean)
}