1
var restoreIpAddresses = function (s) {
2
  const results = [];
3

4
  const go = (str, arr) => {
5
    // if we used every character and have 4 sections, it's a good IP!
6
    if (str.length === 0 && arr.length === 4) {
7
      results.push(arr.join("."));
8
      return;
9
    }
10
    // we already have too many in the array, let's just stop
11
    if (arr.length >= 4) {
12
      return;
13
    }
14
    // chop off next 3 characters and continue recursing
15
    if (
16
      str.length > 2 &&
17
      +str.substring(0, 3) < 256 &&
18
      +str.substring(0, 3) > 0 &&
19
      str[0] !== "0"
20
    ) {
21
      go(str.slice(3), [...arr, str.substring(0, 3)]);
22
    }
23
    // chop off next 2 characters and continue recursing
24
    if (str.length > 1 && +str.substring(0, 2) > 0 && str[0] !== "0") {
25
      go(str.slice(2), [...arr, str.substring(0, 2)]);
26
    }
27
    // chop off next 1 character and continue recursing, in this case, starting with 0 is OK
28
    if (str.length > 0 && +str.substring(0, 1) >= 0) {
29
      go(str.slice(1), [...arr, str.substring(0, 1)]);
30
    }
31
    return;
32
  };
33

34
  go(s, []);
35

36
  return results;
37
};