LeetCode 1942: The Number of the Smallest Unoccupied Chair Solution

Master LeetCode problem 1942 (The Number of the Smallest Unoccupied Chair), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1942. The Number of the Smallest Unoccupied Chair

Medium

Array Hash Table Heap (Priority Queue)

Problem Explanation

Explanation:

We can simulate the process of friends arriving and leaving the party.
We can maintain two priority queues, one for available chairs and one for occupied chairs.
We iterate through the times array in chronological order.
For each friend's arrival, we assign them the smallest available chair.
When a friend leaves, we mark their chair as available again.
We keep track of the chair assigned to the targetFriend and return it at the end.

Time Complexity: O(n log n), where n is the number of friends arriving and leaving. Space Complexity: O(n), where n is the number of friends arriving and leaving.

Solution Code

import java.util.*;

class Solution {
    public int smallestChair(int[][] times, int targetFriend) {
        PriorityQueue<Integer> availableChairs = new PriorityQueue<>();
        PriorityQueue<int[]> occupiedChairs = new PriorityQueue<>((a, b) -> a[1] - b[1]);
        int[] targetFriendTimes = null;

        for (int i = 0; i < times.length; i++) {
            availableChairs.offer(i);
        }

        for (int[] time : times) {
            while (!occupiedChairs.isEmpty() && occupiedChairs.peek()[1] <= time[0]) {
                int chair = occupiedChairs.poll()[0];
                availableChairs.offer(chair);
            }

            int friend = time[0];
            int chair = availableChairs.poll();
            if (friend == times[targetFriend][0]) {
                targetFriendTimes = new int[]{chair, time[1]};
            }
            occupiedChairs.offer(new int[]{chair, time[1]});
        }

        return targetFriendTimes[0];
    }
}

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