Let's say given a number of array, you should print out, all the subet of this array.

Example: [1, 2]

Output:

> ""

> 1
> 2

> 1,2

 

The number of subset should be 2^n... 

 

function print_set(subset) {
  if (subset.length === 0) {
    console.log('empty');
  }
  console.log(subset.filter(Boolean).join(','));
}


function all_subsets(given_array) {

  function helper(given_array, subset, i) {
    if (given_array.length === 0) {
      print_set([]);
    }

    if (i === given_array.length) {
      print_set(subset);
      return;
    }

    // in case of not include the current item
    subset[i] = null
    console.log(`set i: ${i} to null`);
    helper(given_array, subset, i + 1);
    // in case of inlcude the current item
    subset[i] = given_array[i]
    console.log(`set i: ${i} to ${given_array[i]}`);
    helper(given_array, subset, i + 1)
  }
  let subset = new Array(given_array.length);
  helper(given_array, subset, 0);
}

const data = [1, 2];
all_subsets(data);
/**
set i: 0 to null
set i: 1 to null
""
set i: 1 to 2
2
set i: 0 to 1
set i: 1 to null
1
set i: 1 to 2
1
 */