I'm trying to factor

s^3 + 3s^2 + 3s + 1

From pascals triangle I know the answer by looking at it. But when I go to try and factor it showing all work I get stumped.. I can't seem to get (s + 1)^3 when factoring the long way and not just by looking at it.

I've tried grouping, long division, I can't get it. Can anyone show me what I'm missing?