Encode/compress sequence of repeating integers

Question

I have very long integer sequences that look like this (arbitrary length!):

0000000001110002220033333

Now I need some algorithm to convert

Answer 1

Here's a shorter version:

function smush(str) {
  return str.replace(/((.)\2*)/g, function(_, w, x) {
    return x + w.length;
  });
}

edit oh I see you want to encode with php; sorry I don't know that. Here's a decoder in a similar spirit:

function unsmush(str) {
  return str.replace(/(.)(\d+)/g, function(_, x, n) {
    return new Array(parseInt(n, 10) + 1).join(x);
  });
}