Google virtual onsite question:

implement probability(x,t) where x is an integer location on a 1d axis. we start from x=0 with probability of 1. We can go right, left, or stay where we are at each integer time step with probabilities p1, p2, 1-p1-p2. time increments as dt = 1. Every time you move right, left, or stay where you are (every action), time increments 1 unit.