First steps wtih Kattis and Javascript

Here’s how to do basic Kattis tasks in Javascript, using the Node.js dialect.

Environment

To begin use the online environment provided at https://onecompiler.com/nodejs/. There is a simple editor in the left-hand pane, and you can write input in the North–East pane. (Do avoid the online environment at p5.js – there is no way to provide input in that framework because it focusses on different libraries and a different run time environment.)

After solving dozens of Kattis tasks in this setting, you can consider installing a Javascript environment on your own machine. Go to node.js for the runtime environment. You also need an editor to write (and save) code on your machine.

Input, Output, and Solutions

Most Kattis problems ask you to write a program that transforms input (say, 2 2) to output (say, 4).

Output in javascript is printed using console.log(string), so that’s easy. Try to solve hello.

Input is a little bit trickier in Javascript and uses some advanced topics like event handlers. Here’s a few lines of code that abstracts away all of these higher-order concepts and just puts all of input into an array of strings:

const readline = require('readline');
const rl = readline.createInterface({ input: process.stdin, });
const input = []
rl.on('line', (line) => { input.push(line); });
rl.on('close', () => { solve(input) });

function solve(input) {
    // your code goes here
}

The input is now in the array of strings input.

Kvedja

For instance, here is a solution to open.kattis.com/problems/kvedja:

const readline = require('readline');
const rl = readline.createInterface({ input: process.stdin, });
const input = []
rl.on('line', (line) => { input.push(line); });
rl.on('close', () => { solve(input) });

function solve(input) {
    console.log("Kvedja,")
    console.log(input[0])
}

Add Two Numbers

To solve open.kattis.com/problems/addtwonumbers, change the solve function to

function solve(input) {
    let tokens = input[0].split(" ")
    let a = parseInt(tokens[0])
    let b = parseInt(tokens[1])
    console.log(a + b)
}

Note the conversion: input[0] (the first line of input) is a string of space-separated integers. The split(" ")-function turns this into tokens, which has type string[] (“array of strings”). The first element of that array tokens[0] is a string, say "3". The parseInt function turns that into an integer 3.

N-Sum

Here’s nsum:

function solve(input) {
  let tokens = input[1].split(" ")
  let sum = 0;
  for (let i = 0; i < tokens.length; i++) {
    sum += parseInt(tokens[i], 10);
  }
  console.log(sum);
}