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# March LeetCoding Challenge 2021 — Day 19: Keys and Rooms

Today, we will solve the 19th problem of the March LeetCoding Challenge.

## Problem Statement

There are N rooms and you start in room 0. Each room has a distinct number in 0, 1, 2, ..., N-1, and each room may have some keys to access the next room.

Formally, each room i has a list of keys rooms[i], and each key rooms[i][j] is an integer in [0, 1, ..., N-1] where N = rooms.length. A key rooms[i][j] = v opens the room with number v.

Initially, all the rooms start locked (except for room 0).

You can walk back and forth between rooms freely.

Return true if and only if you can enter every room.

Example 1:

``````**Input: **[[1],[2],[3],[]]
**Output: **true
**Explanation:  **
We start in room 0, and pick up key 1.
We then go to room 1, and pick up key 2.
We then go to room 2, and pick up key 3.
We then go to room 3.  Since we were able to go to every room, we return true.
``````

Example 2:

``````**Input: **[[1,3],[3,0,1],[2],[0]]
**Output: **false
**Explanation: **We can't enter the room with number 2.
``````

Note:

1. 1 <= rooms.length <= 1000

2. 0 <= rooms[i].length <= 1000

3. The number of keys in all rooms combined is at most 3000.

## Solution

In this problem, we have to find whether we can visit all the rooms. Initially, the 0-th room is opened, and at every index, we have the keys to go to other rooms. So, we can visualize this problem as a graph-based problem.

Once we enter the 0-th room, we will check for keys in that room. Once we find a key, we directly move to that room and repeat the process. We keep the count of visited rooms in a HashSet. If the size of the HashSet is equal to the number of rooms, we return true else false. We are using breath-first-search to solve this problem.

The code can be found here

# LeetCode

I have been solving Leetcode problems for around a year or so. Suddenly I have developed a passion of writing tutorials for these problems. I am starting with Leetcode problem, in future I will try to make tutorials on Spring,Android,Java,Algorithms and many more.

Follow me on medium - https://sourav-saikia.medium.com
Follow me on dev.to - https://dev.to/sksaikia

The following table contains all the problems with their respective solution tutorials. I will try to add more articles to it soon.

## March LeetCoding Challenge

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