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    1.1.1 • Public • Published

    CodeForces IO

    Small package to mock Codeforces Javascript IO functions.

    Build Test NPM


    npm i @ip-algorithmics/codeforces-io


    Codeforces for Javascript/Typescript uses readline() and print() functions for input and output to the standard input/console.

    How to use

    This library exposes the functions in a manner that allows you to just copy the source code for the submission.

    Importing the functions

    The functions can be imported both as ES6 modules or using the require function. The difference lays in how you access it.

    // using ES6 modules import - you need to have the "module" property set to "commonjs" in the package.json
    import { readline, print } from '@ip-algorithmics/codeforces-io';
    // using require
    const codeForcesIO = require('@ip-algorithmics/codeforces-io');
    const readline = codeForcesIO.readline;
    const print = codeForcesIO.print;
    // alternative
    const { readline, print, console } = require('@ip-algorithmics/codeforces-io');


    This function returns the next line read from the input.txt file from the same folder. You can iterate through the file calling it again.

    let n = readline();
    for (let i = 0; i < n; i++) {
        let x = readline();
        // do something with x

    If you want to change the file path you must wrap the function inside your own.

    import { readline as readlineCustom } from '@ip-algorithmics/codeforces-io';
    function readline() {
        return readlineCustom(filePath); // where filePath is the desired path to your file
    // rest of the code
    // alternatively using require
    const codeForcesIO = require('@ip-algorithmics/codeforces-io');
    const readlineCustom = codeForcesIO.readline;
    const print = codeForcesIO.print;
    function readline() {
        return readlineCustom(filePath); // where filePath is the desired path to your file

    Special mention

    readline() can iterate through the entire file without needing the user to know the number of actual lines. Codeforces provides it for lower level languages like C.

    If you chose to iterate it like this, the end of file will return the empty string('').

    let line;
    while ((line = readline() && line != '')) {
        // do something with line
    // or
    let line = readline();
    while (line != '') {
        // do something with line
        line = readline();


    This function just prints to the console the parameter. It is a glorified console.log that saves whatever is printed in memory. You can then use testOutput() to print to the screen if the test passed or failed.

    let output = 'this is the output';


    This is an optional function reads the output.txt from the same folder and iterates through the print statements to check if they match the outputs. You can set a different path passing it as a parameter.


    If you use Typescript you will notice that the print function is already declared in the DOM library. To circumvent this issue I exported console.log as print and the entire console object as console for the cases where is needed for tracing or debugging.

    Code example

    Statement: given the input, print it

    // input.txt
    This is the input
    import { readline, print } from '@ip-algorithmics/codeforces-io';
    let firstLine = readline();
    print(firstLine); //prints: This is the input

    Statement: given the input - first line is the number of cases, next lines are the number describing geo points separated by comma. Find and print the geo point that is not valid. input.txt



    const { readline, print, testOutput } = require('@ip-algorithmics/codeforces-io');
    let numberOfLines = parseInt(readline(), 10);
    for (let i = 0; i < numberOfLines; i++) {
        let x = readline()
            .map((y) => parseInt(y, 10));
        if ((x[0] < 90 && x[0] > -90) || (x[1] < 90 && x[1] > -90)) {
            print(x[0] + ',' + x[1]);
    testOutput(); // Result Passed

    Solution generator

    You can use this feature in 2 ways:

    • Without installing globally the library using npx @ip-algorithmics/codeforces-io.
    • Installing globally the library npm i -g @ip-algorithmics/codeforces-io and then using cf in the command line.


    • path - the path to the solution. E.g. ./ProblemA. Defaults to ./New Solution.
    • --f or --file - the name of the js/ts file to create. E.g. mainFile. Defaults to index.
    • --js - Uses .js extension instead of .ts
    • --cjs - Uses require instead of ES6 import/export
    • --c or --comment - Adds a comment at the beginning of the file. E.g. the link to the problem.

    Usage examples

    • npx @ip-algorithmics/codeforces-io ./ProblemA --js --cjs
    • cf ./ProblemA --js --cjs
    • cf ./ProblemA
    • cf ./ProblemA --c http://link.to.problem

    Future plans

    • Problem folder generator - generates folder, input.txt, output.txt, index.ts or index.js, in input puts link to problem, and template imports, and test - Completed

    Additional Resources

    Codeforces - How to use Typescript/Javascript like a pro



    Added solution generator capabilities.


    Added testOutput() function.


    npm i @ip-algorithmics/codeforces-io

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