k combinations of N elements. k, n are natural numbers 0<=k<=n. The output is the nessesary number of rows.

index.js

process.stdin.on('readable', () => {
  const v = process.stdin.read();
  if (v !== null) {
    let input = v.toString('utf8').split(" ").map(n => parseInt(n));
    let k = input[0] || 0;
    let n = input[1] || 0;
    //Count of combinations
    let c = 0;

// took here http://e-maxx.ru/algo/generating_combinations
    function nextCombination(position, lasta) {
      for (let p = position; p >= 0; --p) {
        if (lasta[p] < n - k + p) {
          lasta[p]++;
          for (let j = p + 1; j < k; ++j) {
            lasta[j] = lasta[j - 1] + 1;
          }

          process.stdout.write(lasta.join(' ').toString() + '\n');
          c++;
          //next recurtion
          if (lasta[k - 1] < n - 1) {
            nextCombination(k - 1, lasta);

          }
        }

      }

    }


    let lasta = [];
    //the initial combination is first numbers from 0 to k
    for (let i = 0; i < k; i++) {
      lasta.push(i);
    }
    process.stdout.write(lasta.join(' ').toString() + '\n');
    //Start recurtion
    nextCombination(k - 1, lasta);

  }
});

Sample Input 1:

2 3
Sample Output 1:

0 1
0 2
1 2