841. Keys and Rooms
use std::collections::HashSet; use std::collections::VecDeque; /** 841. Keys and Rooms https://leetcode.com/problems/keys-and-rooms/ There are n rooms labeled from 0 to n - 1 and all the rooms are locked except for room 0. Your goal is to visit all the rooms. However, you cannot enter a locked room without having its key. When you visit a room, you may find a set of distinct keys in it. Each key has a number on it, denoting which room it unlocks, and you can take all of them with you to unlock the other rooms. Given an array rooms where rooms[i] is the set of keys that you can obtain if you visited room i, return true if you can visit all the rooms, or false otherwise. Example 1: Input: rooms = [[1],[2],[3],[]] Output: true Explanation: We visit room 0 and pick up key 1. We then visit room 1 and pick up key 2. We then visit room 2 and pick up key 3. We then visit room 3. Since we were able to visit every room, we return true. Example 2: Input: rooms = [[1,3],[3,0,1],[2],[0]] Output: false Explanation: We can not enter room number 2 since the only key that unlocks it is in that room. Constraints: 1. n == rooms.length 2. 2 <= n <= 1000 3. 0 <= rooms[i].length <= 1000 4. 1 <= sum(rooms[i].length) <= 3000 5. 0 <= rooms[i][j] < n 6. All the values of rooms[i] are unique. */ pub struct Solution {} impl Solution { /* Solution: scan each level to check if contains all room num by DFS or BFS; M is size of rooms, N is maximum size of rooms's element; Time:O(M*N), Space:O(N); */ pub fn can_visit_all_rooms(rooms: Vec<Vec<i32>>) -> bool { let mut visited: HashSet<i32> = HashSet::new(); //Self::dfs(0, &rooms, &mut visited); //visited.len() == rooms.len() Self::bfs(0, &rooms, &mut visited) } fn dfs(key: i32, rooms: &Vec<Vec<i32>>, visited: &mut HashSet<i32>) { if visited.contains(&key) { return; } visited.insert(key); for i in &rooms[key as usize] { Self::dfs(*i, rooms, visited) } } /* Use a queue to keep the keys we found in a room, only enqueue the keys not visited yet. Repeat until the queue is empty, and check if size of visited set equals size of rooms. */ fn bfs(key: i32, rooms: &Vec<Vec<i32>>, visited: &mut HashSet<i32>) -> bool { let mut queue: VecDeque<i32> = VecDeque::new(); queue.push_back(0); while !queue.is_empty() { let top = queue.pop_front().unwrap(); visited.insert(top); for i in &rooms[top as usize] { if (visited.contains(i)) { continue; } queue.push_back(*i); } } rooms.len() == visited.len() } }