medium   Probability

2D Paths III

A release-checked medium problem for training Combinatorics.

Question

You are playing a 2D game where your character is trapped in a $6 \times 6$ grid. Your character starts at $(0,0)$ and can only move up and right. There are two power-ups located at $(2,3)$ and $(4,6)$. How many possible paths can your character take to get to $(6,6)$ such that it can collect at least one power-up?

Practice focus

This Probability problem is tagged Combinatorics. State the random variables and conditioning information explicitly, then check the result against boundary cases before opening hints or a solution.

Reviewed questions in this area

easyBaby BoyReviewed

Probability · SIG, DE Shaw

easyBad BagelReviewed

Probability · SIG, Jane Street