non recursive k-combination

generate_k_combination.js

const N = 7;
const M = 4;

const positions = [];
for (let i = 0; i < M; i += 1) {
  positions.push(i);
}

const set = [];
for (let i = 0; i < N; i += 1) {
  set[i] = i + 1;
}

let hasChange = false;
do {
  const result = positions.map(p => set[p]);
  console.log(result);

  // This code works like a calculator
  // it tries to increment the latest positional value, if it succeeds,
  // then it resets all the remaining positions to be in sequential order.
  // if it fails to increment a position it will try to increment the previous position and so on.
  hasChange = false;
  for (let i = M - 1; i >= 0; i -= 1) {
    if (positions[i] - i + M < N) {
      positions[i] += 1;
      hasChange = true;

      for (let j = i + 1; j < M; j += 1) {
        positions[j] = positions[j - 1] + 1;
      }

      break;
    }
  }
} while(hasChange);