# Keys And Rooms Problem

## Description

LeetCode Problem 841.

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:

``````1
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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:

``````1
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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:

• n == rooms.length
• 2 <= n <= 1000
• 0 <= rooms[i].length <= 1000
• 1 <= sum(rooms[i].length) <= 3000
• 0 <= rooms[i][j] < n
• All the values of rooms[i] are unique.

## Sample C++ Code

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class Solution {
public:
bool canVisitAllRooms(vector<vector<int>>& rooms) {
int n = rooms.size();
vector<int> visited(n, 0);
visited[0] = 1;
int r;

stack<int> st;
st.push(0);

while (!st.empty()) {
r = st.top();
st.pop();
for (int i = 0; i < rooms[r].size(); i ++) {
if (visited[rooms[r][i]] == 0) {
visited[rooms[r][i]] = 1;
st.push(rooms[r][i]);
}
}
}

for (auto v : visited) {
if (v == 0)
return false;
}
return true;
}
};
``````