SDE - 1

You are the receptionist at a hotel which has 10 floors, numbered from 0 to 9 and each floor has 26 rooms named from ‘A’ to ‘Z’. Being a receptionist your task is to handle booking queries.

You get booking queries in the form of strings of size 3 where 1st character is ‘+’ means room is booked, or ‘-’ means room is freed. Second character represents the floor of the room i.e, ‘0’ to ‘9’. Third character represents the room name i.e, ‘A’ to ‘Z’.

On booking of each room you collect 1 coin from the customer. After the end of all the booking queries you have to count the number of coins you collected.

You may assume that the list describes a correct sequence of bookings in chronological order i.e., only free rooms can be booked, and only booked rooms can be freed.

For Example:-

Consider booking queries to be ["+1A", "+3E", "-1A", "+4F", "+1A", "-3E"]
+1A: Room A on the 1st floor is booked and you collected 1 coin.
+3E: Room E on the 3rd floor is booked and you collected 1 coin.
-1A: Room A on the 1st floor is freed.
+4F: Room F on the 4th floor is booked and you collected 1 coin.
+1A: Room A on the 1st floor is booked and you collected 1 coin.
-3E: Room E on the 3rd floor is freed.
So you collected 4 coins.

You are given two big numbers ‘A’ and ‘B’ as strings. Your task is to find the product of both the numbers.

Note:

There are no leading zeros in both the strings, except the number 0 itself.
Do not use any built-in Big Integer Library.

For Example:

If, A = 123, and B = 456.
So the product of both numbers will be 56088.

This time our favorite Ninja wants to buy a house. But they are unable to count the number of rooms in the house. So they need your help to count the number of rooms.

Note:

A house is represented by a matrix where “\” and “/” represent a wall and blank space is empty space. We will consider two rooms different if we will be unable to reach another room.

Your task is to return the number of rooms. For a better explanation, see the example.

Example:

Input: 
[
  “ /”
  “/\”
]

Output: 3

Explanation: 2 X 2 house is shown below:

You have been given a board where there are '2' rows and 'N' columns. You have an infinite supply of 2x1 tiles, and you can place a tile in the following ways:

1. Horizontally as 1x2 tile
2. Vertically as 2x1 tile

Count the number of ways to tile the given board using the available tiles.

Note :

The number of ways might be large so output your answer modulo 10^9 + 7.

Here an example of tile and board for 'N' = 4 :

There are 100 closed doors. A cage holding 100 monkeys is placed nearby. Every monkey that visits a door either opens a closed door or closes an open door. The first monkey that is let out of the cage visits and opens all one hundred doors. The second monkey that is released visits doors 2, 4, 6, 8, 10, and so on. The third monkey released visits doors 3, 6, 9, 12, 15, and so on.

After all the monkeys from the cage are released and have opened or closed at least one door, how many doors are left open? (Learn)