Description

You can check your solutions here: https://judge.softuni.bg/Contests/Practice/Index/925.
I. Working with Stacks
1. Reverse Strings
Write program that:
• Reads an input string
• Reverses it using a Stack<T>
• Prints the result back at the terminal
Examples
Input Output
Learning Java avaJ gninraeL
Stacks and Queues seueuQ dna skcatS
Hints
• Use a Stack<string>
• Use the methods Push(), Pop()
2. Simple Calculator
Create a simple calculator that can evaluate simple expressions with only addition and subtraction. There will not be any parentheses.
Solve the problem using a Stack.
Examples
Input Output
2 + 5 + 10 – 2 – 1 14
2 – 2 + 5 5
Hints
• Use a Stack<string>
• You can either o add the elements and then Pop() them out o or Push() them and reverse the stack
3. Decimal to Binary Converter
Create a simple program that can convert a decimal number to its binary representation. Implement an elegant solution using a Stack.
Print the binary representation back at the terminal.
Examples
Input Output
10 1010
1024 10000000000
Hints
• If the given number is 0, just print 0
• Else, while the number is greater than zero, divide it by 2 and push the remainder into the stack
• When you are done dividing, pop all remainders from the stack – that is the binary representation
4. Matching Brackets
We are given an arithmetic expression with brackets. Scan through the string and extract each sub-expression.
Print the result back at the terminal.
Examples
Input Output
1 + (2 – (2 + 3) * 4 / (3 + 1)) * 5 (2 + 3)
(3 + 1)
(2 – (2 + 3) * 4 / (3 + 1))
(2 + 3) – (2 + 3) (2 + 3)
(2 + 3)
Hints
• Scan through the expression searching for brackets o If you find an opening bracket, push the index into the stack o If you find a closing bracket pop the topmost element from the stack. This is the index of the opening bracket.
o Use the current and the popped index to extract the sub-expression
II. Working with Queues
5. Hot Potato
Hot potato is a game in which children form a circle and start passing a hot potato. The counting starts with the fist kid. Every nth toss the child left with the potato leaves the game. When a kid leaves the game, it passes the potato along. This continues until there is only one kid left.
Create a program that simulates the game of Hot Potato. Print every kid that is removed from the circle. In the end, print the kid that is left last.
Examples
Input Output
Mimi Pepi Toshko 2 Removed Pepi
Removed Mimi
Last is Toshko
Gosho Pesho Misho Stefan Krasi 10 Removed Krasi
Removed Pesho
Removed Misho
Removed Gosho
Last is Stefan
Gosho Pesho Misho Stefan Krasi 1 Removed Gosho
Removed Pesho
Removed Misho
Removed Stefan
Last is Krasi
6. Traffic Light
Create a program that simulates the queue that forms during a traffic jam. During a traffic jam only N cars can pass the crossroads when the light goes green. Then the program reads the vehicles that arrive one by one and adds them to the queue. When the light goes green N number of cars pass the crossroads and for each a message “{car} passed!” is displayed. When the “end” command is given, terminate the program and display a message with the total number of cars that passed the crossroads.
Input
• On the first line you will receive N – the number of cars that can pass during a green light
• On the next lines, until the “end” command is given, you will receive commands – a single string, either a car or “green”
Output
• Every time the “green” command is given, print out a message for every car that passes the crossroads in the format “{car} passed!”
• When the “end” command is given, print out a message in the format “{number of cars} cars passed the crossroads.”
Examples
Input Output
4
Hummer H2
Audi
Lada
Tesla
Renault
Trabant
Mercedes MAN Truck green green Tesla
Renault Trabant end Hummer H2 passed!
Audi passed!
Lada passed!
Tesla passed!
Renault passed!
Trabant passed!
Mercedes passed!
MAN Truck passed!
8 cars passed the crossroads.
3
Pesho’s car
Gosho’s car Pesho’s car passed!
Gosho’s car passed!
Mercedes CLS passed!
Mercedes CLS Nekva troshka
green BMW X5 green end Nekva troshka passed!
BMW X5 passed!
5 cars passed the crossroads.