# 1942. The Number of the Smallest Unoccupied Chair import heapq """ there is a party where 'n' friends numbered from 0 to 'n - 1' are attending. there is an infinite number of chairs in this part 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] = [arrival[i], leaving[i]]' indicating the arrival and leaving times of the i'th friend respectively. and an integer 'targetFriend'. all arrival times are distinct. return the chair number that the friend numbered 'targetFriend' will sit on. """ class Solution(object): def smallestChair(self, times, targetFriend): """ :type times: List[List[int]] :type targetFriend: int :rtype: int """ order = sorted(range(len(times)), key=lambda x: times[x][0]) empty, taken = list(range(len(times))), [] for i in order: arrive, leave = times[i] while taken and taken[0][0] <= arrive: heapq.heappush(empty, heapq.heappop(taken)[1]) seat = heapq.heappop(empty) if i == targetFriend: return seat heapq.heappush(taken, (leave, seat)) if __name__ == "__main__": obj = Solution() print(obj.smallestChair(times=[[1, 4], [2, 3], [4, 6]], targetFriend=1)) print(obj.smallestChair(times=[[3, 10], [1, 5], [2, 6]], targetFriend=0))