Solution for https://www.hackerearth.com/practice/algorithms/searching/linear-search/practice-problems/algorithm/wet-clothes-625348cf/

index.js

process.stdin.resume();
process.stdin.setEncoding("utf-8");
var stdin_input = "";

process.stdin.on("data", function (input) {
    stdin_input += input; // Reading input from STDIN
});

process.stdin.on("end", function () {
   main(stdin_input); // Execute our entrypoint when we've finished reading the input
});

/**
 * Out main entrypoint to execute.
 * 
 * Built-in functions used:
 * * String.prototype.split: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split
 * * Array.prototype.map: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map
 * * Array.prototype.filter: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter
 * * parseInt: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt
 */
function main(input) {
    const lines = input.split('\n'); // Split our input based on new line.

    const rainfallTimes = parseStringOfNumbers(lines[1]); // Parse the second line of inputs to capture the rainfall times.

    const dryingTimes = parseStringOfNumbers(lines[2]) // Parse the third line of inputs to capture the drying time of each piece of clothing on the line.

    const largestGap = findLargestGap(rainfallTimes)

    process.stdout.write(dryingTimes.filter((dryingTime) => dryingTime <= largestGap).length)
}

/**
 * All of our input lines are space separated integers in base 10. This will parse them into an array of numbers.
 */
function parseStringOfNumbers(stringOfNumbers) {
    return stringOfNumbers.split(' ').map((val) => parseInt(val, 10)); 
}

/**
 * Since we know we can grab ALL dry clothes on any given pass, we only need to know
 * the largest available gap in rainfall.
 */
function findLargestGap(rainTimes) {
    let currentTime = rainTimes[0] // We know that we are beginning at the first time index.
    let largestGap = 0;
    
    for (let i = 1; i < rainTimes.length; i++) {
        const nextRainTime = rainTimes[i];
        const gap = nextRainTime - currentTime;

        if (gap > largestGap) {
            largestGap = gap;
        }
        
        currentTime = nextRainTime; // Prepare for our next iteration of the loop.
    }

    return largestGap;
}

How do you know that or how does a developer determine which build in functions to use to handle a particular problem ?
i saw that String.prototype.split''''' Array.prototype.map:''''' Array.prototype.filter:''''''' parseInt: are used

line 31 process.stdout.write(dryingTimes.filter((dryingTime) => dryingTime <= largestGap).length) // print out drytime using the condition inside d bracket .