How can I get the smallest number, not in an array, in a functional programming fashion with lo-dash?

Question

I have an array...

[8, 2, 5, 3, 0, 9, 1, 6, 7]

How do I get the smallest number, not listed in the array? 4 in this case.

The only thing I can think of is, but I would like to get rid of the while loop if I could.

var list = [8, 2, 5, 3, 9, 1, 6, 7];
var num = -1;
var done = false;
while (!done) {
  num++;
  if(!_.contains(list, num)) {
    done = true;
  }
}

Answer 1

You could sort the array in n lg n time and start at the beginning and find the first gap.

This solution solves for the lowest number between the min and max. Otherwise, computationally, yours Is the best.

Answer 2

Try this:

function findLowest(n, xs) {
    return xs.indexOf(n) < 0 ? n : findLowest(n + 1, xs);
}

Now all you need to do is:

var n = findLowest(0, [8, 2, 5, 3, 0, 9, 1, 6, 7]);

alert(n); // 4

See the demo for yourself: http://jsfiddle.net/9pXGR/

The findLowest function will find the lowest number not in the list starting from a given number n.