Last updated: Sun Jun 16 at 6:41:46 PM PST

Variables and Data Types

  • Java
    • Declaring variables
String city  = "Las Vegas";
int day = 31;
double degrees = 98.9;
char grade = 'A';
boolean passedAPExam = true;
  • Types of variables: int, double, char, boolean, etc.
  • Type casting: converting from one primitive type to another
double myDouble = 9.78d;
int myInt = (int) myDouble; // Manual casting: double to int
  • Python
    • Variables and dynamic typing
    • Basic data types: int, float, str, bool
    • Type conversion

Control Structures

  • Java
    • Conditional Statements: if, if-else, switch
int age = 16;
bool hasLicense = true;

if (age >= 16 && hasLicense) {
  System.out.println("You can drive!");
} else {
  System.out.println("Ride the bus lol");
}
  • Loops: for, while, do-while

for (int i = 0; i < VALUE; i++) {
  // DO SOMETHING
}


while (!gameOver) {
  keepPlaying();
}

int i = 0;
do {
  System.out.println(i);
  i++;
} 

while (i <= 5);
  • Python
    • Conditional Statements: if, elif, else
    • Loops: for, while

Functions and Methods

  • Java
    • Defining methods
[access modifier] [return type] [name]([parameters]) {
  // TO DO...
}

public int square(int n) {
  return n * n;
}
  • Method calling

obj.methodName();

  • Return types and parameters

  • Python

    • Defining functions
    • Function calling
    • Return values and parameters

Data Structures

  • Java
    • Arrays
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
int[] myNum - {10, 20, 30, 40};
  • ArrayLists

First you’ll import the ArrayList class from the java.util package.

import java.util.ArrayList;

ArrayList<String> cars = new ArrayList<String>(); 
cars.add("Volvo");
cars.add("BMW");
cars.add("Ford");
cars.add(0, "Mazda"); // Insert element at the beginning of the list (0)
System.out.println(cars);
  • HashMaps

HashMaps in Java are similar to dictionaries in Python —they’re for storing items in key - value pairs.

import java.util.HashMap; // import the HashMap class

HashMap<String, String> capitalCities = new HashMap<String, String>();
// Add keys and values (Country, City)
capitalCities.put("England", "London");
capitalCities.put("Germany", "Berlin");
capitalCities.put("Norway", "Oslo");
capitalCities.put("USA", "Washington DC");
System.out.println(capitalCities);
  • Python
    • Lists
    • Dictionaries
    • Sets

Object-Oriented Programming

  • Java
    • Understanding classes and objects
    • Constructors
    • Encapsulation, Inheritance, and Polymorphism

Classes

A class called Main in a file called Main.java with a main method.


public Class Main {
	public static void main(String[] args) {
		
	}
}
  • Python
    • Classes and objects
    • Constructors
    • Inheritance and method overriding

Error Handling

  • Java
    • Try-catch blocks
public class Main {
  public static void main(String[ ] args) {
    try {
      int[] myNumbers = {1, 2, 3};
      System.out.println(myNumbers[10]);
    } catch (Exception e) {
      System.out.println("Something went wrong.");
    }
  }
}
  • Finally block
  • Creating custom exceptions
try {
    System.out.println("The count is " + Integer.parseInt(count));
} catch (NumberFormatException e) {
    System.out.println("No count");
} finally {
    System.out.println("In finally");
}
  • Python
    • Try-except block
    • Finally and else clauses
    • Raising exceptions

Libraries and APIs

  • Java
    • Using standard libraries (e.g., java.util)
    • Reading from and writing to files
  • Python
    • Using standard libraries (e.g., sys, os)
    • File handling (open, read, write, close)

Choosing your assignments

  • Java
    • One USACO problem (Bronze Level)
    • One USACO problem (Silver Level)
    • One USACO problem (Gold Level)
  • Python
    • One USACO problem (Bronze Level)
    • One USACO problem (Silver Level)
    • One USACO problem (Gold Level)

Recommendations:

I recommend you solve at least one of the following problems using both languages. If you visit the USACO Guide problems page, you should be able to find solutions for these problems. Only use them to go over your work!

USACO 2016 January Contest, Bronze - Problem 1. Promotion Counting

USACO 2020 January Contest, Bronze - Problem 1. Word Processor

USACO 2016 December Contest, Silver - Problem 1. Counting Haybales

Assignment

BRONZE

Hungry Cow Feb 2023

SILVER

Bakery Feb 23

GOLD

Piling Papers Feb 23

TEMPLATE for USACO problems