LeetCode 1912. Design Movie Rental System Solution in Java, C++, Python & Go | Explanation + Code

Description

You have a movie renting company consisting of n shops. You want to implement a renting system that supports searching for, booking, and returning movies. The system should also support generating a report of the currently rented movies.

Each movie is given as a 2D integer array entries where entries[i] = [shopi, moviei, pricei] indicates that there is a copy of movie moviei at shop shopi with a rental price of pricei. Each shop carries at most one copy of a movie moviei.

The system should support the following functions:

• Search: Finds the cheapest 5 shops that have an unrented copy of a given movie. The shops should be sorted by price in ascending order, and in case of a tie, the one with the smaller shopi should appear first. If there are less than 5 matching shops, then all of them should be returned. If no shop has an unrented copy, then an empty list should be returned.
• Rent: Rents an unrented copy of a given movie from a given shop.
• Drop: Drops off a previously rented copy of a given movie at a given shop.
• Report: Returns the cheapest 5 rented movies (possibly of the same movie ID) as a 2D list res where res[j] = [shopj, moviej] describes that the jth cheapest rented movie moviej was rented from the shop shopj. The movies in res should be sorted by price in ascending order, and in case of a tie, the one with the smaller shopj should appear first, and if there is still tie, the one with the smaller moviej should appear first. If there are fewer than 5 rented movies, then all of them should be returned. If no movies are currently being rented, then an empty list should be returned.

Implement the MovieRentingSystem class:

• MovieRentingSystem(int n, int[][] entries) Initializes the MovieRentingSystem object with n shops and the movies in entries.
• List<Integer> search(int movie) Returns a list of shops that have an unrented copy of the given movie as described above.
• void rent(int shop, int movie) Rents the given movie from the given shop.
• void drop(int shop, int movie) Drops off a previously rented movie at the given shop.
• List<List<Integer>> report() Returns a list of cheapest rented movies as described above.

Note: The test cases will be generated such that rent will only be called if the shop has an unrented copy of the movie, and drop will only be called if the shop had previously rented out the movie.

 

Example 1:

Input
["MovieRentingSystem", "search", "rent", "rent", "report", "drop", "search"]
[[3, [[0, 1, 5], [0, 2, 6], [0, 3, 7], [1, 1, 4], [1, 2, 7], [2, 1, 5]]], [1], [0, 1], [1, 2], [], [1, 2], [2]]
Output
[null, [1, 0, 2], null, null, [[0, 1], [1, 2]], null, [0, 1]]

Explanation
MovieRentingSystem movieRentingSystem = new MovieRentingSystem(3, [[0, 1, 5], [0, 2, 6], [0, 3, 7], [1, 1, 4], [1, 2, 7], [2, 1, 5]]);
movieRentingSystem.search(1);  // return [1, 0, 2], Movies of ID 1 are unrented at shops 1, 0, and 2. Shop 1 is cheapest; shop 0 and 2 are the same price, so order by shop number.
movieRentingSystem.rent(0, 1); // Rent movie 1 from shop 0. Unrented movies at shop 0 are now [2,3].
movieRentingSystem.rent(1, 2); // Rent movie 2 from shop 1. Unrented movies at shop 1 are now [1].
movieRentingSystem.report();   // return [[0, 1], [1, 2]]. Movie 1 from shop 0 is cheapest, followed by movie 2 from shop 1.
movieRentingSystem.drop(1, 2); // Drop off movie 2 at shop 1. Unrented movies at shop 1 are now [1,2].
movieRentingSystem.search(2);  // return [0, 1]. Movies of ID 2 are unrented at shops 0 and 1. Shop 0 is cheapest, followed by shop 1.

 

Constraints:

• 1 <= n <= 3 * 105
• 1 <= entries.length <= 105
• 0 <= shopi < n
• 1 <= moviei, pricei <= 104
• Each shop carries at most one copy of a movie moviei.
• At most 105 calls in total will be made to search, rent, drop and report.

Solutions

Solution 1: Ordered Set

We define an ordered set available, where available[movie] stores a list of all shops that have not rented out the movie movie. Each element in the list is (price, shop), sorted in ascending order by price, and if prices are equal, by shop in ascending order.

Additionally, we define a hash map price_map, where price_map[f(shop, movie)] stores the rental price of movie movie in shop shop.

We also define an ordered set rented, which stores all rented movies as (price, shop, movie), sorted in ascending order by price, then by shop, and if both are equal, by movie.

For the MovieRentingSystem(n, entries) operation, we iterate through entries and add each shop's movie information to both available and price_map. The time complexity is O(m log m), where m is the length of entries.

For the search(movie) operation, we return the shop IDs of the first 5 shops in available[movie]. The time complexity is O(1).

For the rent(shop, movie) operation, we remove (price, shop) from available[movie] and add (price, shop, movie) to rented. The time complexity is O(log m).

For the drop(shop, movie) operation, we remove (price, shop, movie) from rented and add (price, shop) back to available[movie]. The time complexity is O(log m).

For the report() operation, we return the shop and movie IDs of the first 5 rented movies in rented. The time complexity is O(1).

The space complexity is O(m), where m is the length of entries.

PythonJavaC++Go

class MovieRentingSystem: def __init__(self, n: int, entries: List[List[int]]): self.available = defaultdict(lambda: SortedList()) self.price_map = {} for shop, movie, price in entries: self.available[movie].add((price, shop)) self.price_map[self.f(shop, movie)] = price self.rented = SortedList() def search(self, movie: int) -> List[int]: return [shop for _, shop in self.available[movie][:5]] def rent(self, shop: int, movie: int) -> None: price = self.price_map[self.f(shop, movie)] self.available[movie].remove((price, shop)) self.rented.add((price, shop, movie)) def drop(self, shop: int, movie: int) -> None: price = self.price_map[self.f(shop, movie)] self.rented.remove((price, shop, movie)) self.available[movie].add((price, shop)) def report(self) -> List[List[int]]: return [[shop, movie] for _, shop, movie in self.rented[:5]] def f(self, shop: int, movie: int) -> int: return shop << 30 | movie # Your MovieRentingSystem object will be instantiated and called as such: # obj = MovieRentingSystem(n, entries) # param_1 = obj.search(movie) # obj.rent(shop,movie) # obj.drop(shop,movie) # param_4 = obj.report()(code-box)

class MovieRentingSystem { private Map<Integer, TreeSet<int[]>> available = new HashMap<>(); private Map<Long, Integer> priceMap = new HashMap<>(); private TreeSet<int[]> rented = new TreeSet<>((a, b) -> { if (a[0] != b[0]) { return a[0] - b[0]; } if (a[1] != b[1]) { return a[1] - b[1]; } return a[2] - b[2]; }); public MovieRentingSystem(int n, int[][] entries) { for (int[] entry : entries) { int shop = entry[0], movie = entry[1], price = entry[2]; available .computeIfAbsent(movie, k -> new TreeSet<>((a, b) -> { if (a[0] != b[0]) { return a[0] - b[0]; } return a[1] - b[1]; })) .add(new int[] {price, shop}); priceMap.put(f(shop, movie), price); } } public List<Integer> search(int movie) { List<Integer> res = new ArrayList<>(); if (!available.containsKey(movie)) { return res; } int cnt = 0; for (int[] item : available.get(movie)) { res.add(item[1]); if (++cnt == 5) { break; } } return res; } public void rent(int shop, int movie) { int price = priceMap.get(f(shop, movie)); available.get(movie).remove(new int[] {price, shop}); rented.add(new int[] {price, shop, movie}); } public void drop(int shop, int movie) { int price = priceMap.get(f(shop, movie)); rented.remove(new int[] {price, shop, movie}); available.get(movie).add(new int[] {price, shop}); } public List<List<Integer>> report() { List<List<Integer>> res = new ArrayList<>(); int cnt = 0; for (int[] item : rented) { res.add(Arrays.asList(item[1], item[2])); if (++cnt == 5) { break; } } return res; } private long f(int shop, int movie) { return ((long) shop << 30) | movie; } } /** * Your MovieRentingSystem object will be instantiated and called as such: * MovieRentingSystem obj = new MovieRentingSystem(n, entries); * List<Integer> param_1 = obj.search(movie); * obj.rent(shop,movie); * obj.drop(shop,movie); * List<List<Integer>> param_4 = obj.report(); */(code-box)

class MovieRentingSystem { private: unordered_map<int, set<pair<int, int>>> available; // movie -> {(price, shop)} unordered_map<long long, int> priceMap; set<tuple<int, int, int>> rented; // {(price, shop, movie)} long long f(int shop, int movie) { return ((long long) shop << 30) | movie; } public: MovieRentingSystem(int n, vector<vector<int>>& entries) { for (auto& e : entries) { int shop = e[0], movie = e[1], price = e[2]; available[movie].insert({price, shop}); priceMap[f(shop, movie)] = price; } } vector<int> search(int movie) { vector<int> res; if (!available.count(movie)) { return res; } int cnt = 0; for (auto& [price, shop] : available[movie]) { res.push_back(shop); if (++cnt == 5) { break; } } return res; } void rent(int shop, int movie) { int price = priceMap[f(shop, movie)]; available[movie].erase({price, shop}); rented.insert({price, shop, movie}); } void drop(int shop, int movie) { int price = priceMap[f(shop, movie)]; rented.erase({price, shop, movie}); available[movie].insert({price, shop}); } vector<vector<int>> report() { vector<vector<int>> res; int cnt = 0; for (auto& [price, shop, movie] : rented) { res.push_back({shop, movie}); if (++cnt == 5) { break; } } return res; } }; /** * Your MovieRentingSystem object will be instantiated and called as such: * MovieRentingSystem* obj = new MovieRentingSystem(n, entries); * vector<int> param_1 = obj->search(movie); * obj->rent(shop,movie); * obj->drop(shop,movie); * vector<vector<int>> param_4 = obj->report(); */(code-box)

type MovieRentingSystem struct { available map[int]*treeset.Set // movie -> (price, shop) priceMap map[int64]int rented *treeset.Set // (price, shop, movie) } func Constructor(n int, entries [][]int) MovieRentingSystem { // comparator for (price, shop) cmpAvail := func(a, b any) int { x := a.([2]int) y := b.([2]int) if x[0] != y[0] { return x[0] - y[0] } return x[1] - y[1] } // comparator for (price, shop, movie) cmpRented := func(a, b any) int { x := a.([3]int) y := b.([3]int) if x[0] != y[0] { return x[0] - y[0] } if x[1] != y[1] { return x[1] - y[1] } return x[2] - y[2] } mrs := MovieRentingSystem{ available: make(map[int]*treeset.Set), priceMap: make(map[int64]int), rented: treeset.NewWith(cmpRented), } for _, e := range entries { shop, movie, price := e[0], e[1], e[2] if _, ok := mrs.available[movie]; !ok { mrs.available[movie] = treeset.NewWith(cmpAvail) } mrs.available[movie].Add([2]int{price, shop}) mrs.priceMap[f(shop, movie)] = price } return mrs } func (this *MovieRentingSystem) Search(movie int) []int { res := []int{} if _, ok := this.available[movie]; !ok { return res } it := this.available[movie].Iterator() it.Begin() cnt := 0 for it.Next() && cnt < 5 { pair := it.Value().([2]int) res = append(res, pair[1]) cnt++ } return res } func (this *MovieRentingSystem) Rent(shop int, movie int) { price := this.priceMap[f(shop, movie)] this.available[movie].Remove([2]int{price, shop}) this.rented.Add([3]int{price, shop, movie}) } func (this *MovieRentingSystem) Drop(shop int, movie int) { price := this.priceMap[f(shop, movie)] this.rented.Remove([3]int{price, shop, movie}) this.available[movie].Add([2]int{price, shop}) } func (this *MovieRentingSystem) Report() [][]int { res := [][]int{} it := this.rented.Iterator() it.Begin() cnt := 0 for it.Next() && cnt < 5 { t := it.Value().([3]int) res = append(res, []int{t[1], t[2]}) cnt++ } return res } func f(shop, movie int) int64 { return (int64(shop) << 30) | int64(movie) } /** * Your MovieRentingSystem object will be instantiated and called as such: * obj := Constructor(n, entries); * param_1 := obj.Search(movie); * obj.Rent(shop,movie); * obj.Drop(shop,movie); * param_4 := obj.Report(); */(code-box)