There are n cars on an infinitely long road. The cars are numbered from 0 to n - 1 from left to right and each car is present at a unique point. You are given a 0-indexed string directions of length n. directions[i] can be either 'L', 'R', or 'S' de

countCollisions.js

/**
 * @param {string} directions
 * @return {number}
 */
var countCollisions = function(directions) {
    // Step 1: Convert string to array for easier handling
    let arr = directions.split('');
    
    // Step 2: Remove cars that will never collide
    // Trim leading 'L' cars (they move left off the road)
    let i = 0;
    while (i < arr.length && arr[i] === 'L') {
        i++;
    }
    
    // Trim trailing 'R' cars (they move right off the road)
    let j = arr.length - 1;
    while (j >= 0 && arr[j] === 'R') {
        j--;
    }
    
    // Step 3: Count collisions in the remaining substring
    // Every 'L' or 'R' inside this range will eventually collide
    let collisions = 0;
    for (let k = i; k <= j; k++) {
        if (arr[k] === 'L' || arr[k] === 'R') {
            collisions++;
        }
    }
    
    return collisions;
};