8th January 2021

1. 30.3

2. 31.6

3. 32.3

4. 33.3

# Technical

Which of the join operations do not preserve non matched tuples?

1. Left outer join

2. Right outer join

3. Inner join

4. Natural join

Explanation: INNER JOIN: Returns all rows when there is at least one match in BOTH tables.

# Coding Question

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: [,,,[]] 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],,] Output: false Explanation: We can't enter the room with number 2. `

Note:

1 <= rooms.length <= 1000

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

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

# Solution:

`bool canVisitAllRooms(vector<vector<int>>& room) {      vector<int>v(room.size(),0);        queue<int>q;        q.push(0);        while(!q.empty())        {            int r=q.front();                q.pop();            if(!v[r])            {                v[r]=1;                for(int i=0;i<room[r].size();i++)                    q.push(room[r][i]);            }        }        for(int i=0;i<room.size();i++)            if(!v[i])                return false;        return true;}`