Move Until Obstacle Game Using Java

Lesson 3

Introduction

Welcome! This lesson involves a thrilling task that combines basic operations with array manipulation in Java. We will be implementing a "Move Until Obstacle" game using an integer array. Visualize yourself as a game developer, and get ready to delve into the exciting world of problem-solving!

Task Statement

In the "Move Until Obstacle" game, the player begins at the start of a linear ArrayList of integers. The number at each position indicates how many steps a player can move to the right. An obstacle number is one upon which the player cannot land. The goal is to move as far to the right as possible until either an obstacle stops the player or the player reaches the end of the ArrayList.

Your function, public static int solution(ArrayList<Integer> numbers, int obstacle), should tally and return the number of moves needed to reach the end of the ArrayList without encountering an obstacle. If the player encounters an obstacle, the function should return the index at which this obstacle lies.

For example, if the function receives the input: numbers = new ArrayList<>(Arrays.asList(2, 3, 3, 4, 2, 4)) and obstacle = 4, it should return 5. This is because the player starts at the 0th index, takes 2 steps as indicated by the number at the 0th index (landing on the 2nd index), and then takes 3 more steps as indicated by the number at the 2nd index to land on the 5th index, which is the obstacle 4.

If the function receives the following input: numbers = new ArrayList<>(Arrays.asList(4, 1, 2, 2, 4, 2, 2)) and obstacle = 2, the output should be 2. The player starts at the 0th index, takes 4 steps, lands on the 4th index, then takes 4 more steps, which brings the player outside the ArrayList, so the total number of steps the player takes is 2.

Solution Building: Step 1

Our first step is to ensure we have variables to track the player, i.e., their current position and the moves they've taken so far. We'll name them position and moves, initializing both to 0:

Java
1public static int solution(ArrayList<Integer> numbers, int obstacle) {
2    int position = 0;
3    int moves = 0;

Solution Building: Step 2 - Main Loop

Next, we'll use a while loop to iterate over the ArrayList. It continues as long as position is less than the size of the ArrayList numbers, which we obtain using numbers.size():

Java
1public static int solution(ArrayList<Integer> numbers, int obstacle) {
2    int position = 0;
3    int moves = 0;
4    while (position < numbers.size()) {

Solution Building: Step 3 - Obstacle Check

During each iteration, we need to check whether the player has encountered an obstacle. If so, we should return the position at which this obstacle is located:

Java
1public static int solution(ArrayList<Integer> numbers, int obstacle) {
2    int position = 0;
3    int moves = 0;
4    while (position < numbers.size()) {
5        if (numbers.get(position) == obstacle) {
6            return position;
7        }

Solution Building: Step 4 - Move Player and Increment Steps

If the current number is not an obstacle, the player proceeds. The number of steps taken corresponds to the value at the current position. We add this to position and increment moves:

Java
1public static int solution(ArrayList<Integer> numbers, int obstacle) {
2    int position = 0;
3    int moves = 0;
4    while (position < numbers.size()) {
5        if (numbers.get(position) == obstacle) {
6            return position;
7        }
8        moves++;
9        position += numbers.get(position);
10    }

Final Solution: Outside the Loop

Once the loop ends, the player either has reached the end of the ArrayList or has encountered an obstacle. If the player managed to navigate the entirety of the ArrayList without encountering an obstacle, we want to return the total number of moves:

The complete function looks like this:

Java
1import java.util.ArrayList;
2import java.util.Arrays;
3
4public class MoveUntilObstacleGame {
5    public static int solution(ArrayList<Integer> numbers, int obstacle) {
6        int position = 0;
7        int moves = 0;
8        
9        while (position < numbers.size()) {
10            // Check for obstacle at the current position
11            if (numbers.get(position) == obstacle) {
12                return position;  // Return the index of the obstacle
13            }
14            // Increment moves and update position
15            moves++;
16            position += numbers.get(position);  // Move to the next position
17        }
18        
19        // If loop ends without obstacles, return total moves taken
20        return moves;
21    }
22
23    public static void main(String[] args) {
24        System.out.println(solution(new ArrayList<>(Arrays.asList(2, 3, 3, 4, 2, 4)), 4));
25    }
26}

Lesson Summary

Congratulations on successfully implementing the "Move Until Obstacle" game using Java! You've navigated the challenges of this task by applying basic ArrayList manipulation concepts and operations with numbers in Java. Celebrate your achievements, but don't stop there! Up next, we have practice sessions filled with similar exercises to reinforce your understanding and skills. So, gear up and let's keep moving!

Enjoy this lesson? Now it's time to practice with Cosmo!

Practice is how you turn knowledge into actual skills.