Move Until Obstacle Game Using Java

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

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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

import java.util.ArrayList;
import java.util.Arrays;

public class MoveUntilObstacleGame {
    public static int solution(ArrayList<Integer> numbers, int obstacle) {
        int position = 0;
        int moves = 0;
        
        while (position < numbers.size()) {
            // Check for obstacle at the current position
            if (numbers.get(position) == obstacle) {
                return position;  // Return the index of the obstacle
            }
            // Increment moves and update position
            moves++;
            position += numbers.get(position);  // Move to the next position
        }
        
        // If loop ends without obstacles, return total moves taken
        return moves;
    }

    public static void main(String[] args) {
        System.out.println(solution(new ArrayList<>(Arrays.asList(2, 3, 3, 4, 2, 4)), 4));
    }
}

import java.util.ArrayList;
import java.util.Arrays;

public class MoveUntilObstacleGame {
    public static int solution(ArrayList<Integer> numbers, int obstacle) {
        int position = 0;
        int moves = 0;
        
        while (position < numbers.size()) {
            // Check for obstacle at the current position
            if (numbers.get(position) == obstacle) {
                return position;  // Return the index of the obstacle
            }
            // Increment moves and update position
            moves++;
            position += numbers.get(position);  // Move to the next position
        }
        
        // If loop ends without obstacles, return total moves taken
        return moves;
    }

    public static void main(String[] args) {
        System.out.println(solution(new ArrayList<>(Arrays.asList(2, 3, 3, 4, 2, 4)), 4));
    }
}

Introduction

Task Statement

Solution Building: Step 1

Solution Building: Step 2 - Main Loop

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Solution Building: Step 3 - Obstacle Check

Solution Building: Step 4 - Move Player and Increment Steps

Final Solution: Outside the Loop

Lesson Summary