Move Until Obstacle in JavaScript

Introduction

Welcome! This lesson involves a thrilling task that combines basic operations with array manipulation in JavaScript. 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 array 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 array. Your function, function solution(numbers, obstacle), should tally and return the number of moves needed to reach the end of the array 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 = [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 = [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 array. 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 : JavaScript function solution(numbers, obstacle) {let position = 0; let moves = 0;

Solution Building: Step 2 - Main Loop

Next, we'll use a while loop to iterate over the array. It continues as long as position is less than the size of the array numbers, which we obtain using numbers.length : JavaScript function solution(numbers, obstacle) {let position = 0; let moves = 0; while (position < numbers.length) {

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Final Solution: Outside the Loop

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

The complete function looks like this:

JavaScript

function solution(numbers, obstacle) {
    let position = 0;
    let moves = 0;

    while (position < numbers.length) {
        // Check for an obstacle at the current position
        if (numbers[position] === obstacle) {
            return position;  // Return the index of the obstacle
        }
        // Increment moves and update position
        moves++;
        position += numbers[position];  // Move to the next position
    }

    // If loop ends without obstacles, return total moves taken
    return moves;
}

// Example usage
// The obstacle (4) is first encountered at index 5,
// so the output of the following is 5 (the index of the obstacle).
console.log(solution([2, 3, 3, 4, 2, 4], 4));

// Here, the player never lands on the obstacle (2)
// before leaving the array, so the output is 2 (the total number of moves).
console.log(solution([4, 1, 2, 2, 4, 2, 2], 2));

function solution(numbers, obstacle) {
    let position = 0;
    let moves = 0;

    while (position < numbers.length) {
        // Check for an obstacle at the current position
        if (numbers[position] === obstacle) {
            return position;  // Return the index of the obstacle
        }
        // Increment moves and update position
        moves++;
        position += numbers[position];  // Move to the next position
    }

    // If loop ends without obstacles, return total moves taken
    return moves;
}

// Example usage
// The obstacle (4) is first encountered at index 5,
// so the output of the following is 5 (the index of the obstacle).
console.log(solution([2, 3, 3, 4, 2, 4], 4));

// Here, the player never lands on the obstacle (2)
// before leaving the array, so the output is 2 (the total number of moves).
console.log(solution([4, 1, 2, 2, 4, 2, 2], 2));

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