Grid Search and Shortest Paths

Grid and graph search comes up at Waymo more than any other coding topic, which fits the work. A car plans routes over a road graph, and a lot of the code around it reads occupancy grids. The five problems below each come down to breadth-first search or Dijkstra.

One has come up in a phone screen and again in an onsite, and phone screens have asked two more. Once the edges carry drive times, you move from a plain queue to Dijkstra. The hardest of the set came from an ML onsite.

Settle two questions before you code. What counts as a node, and does every edge cost the same? Equal costs mean a plain queue, and drive times on the edges mean a heap. Say which one you chose and why. Then mark a cell as seen when it enters the queue, so no cell gets counted twice.

WaymoPremium lesson · Coding round

The 5 Waymo problems are below.

1. 1A Premium questionCoding · Hard · Frequently asked
2. 2A Premium questionCoding · Medium
3. 3A Premium questionCoding · Medium

+ 2 more in this lesson

Each with hints, the follow-up and a tested solution.

Get the Waymo questions

$49 a year · all 100 companies · cancel anytime

From 20,000+ candidate reports, forum threads behind logins and write-ups in Chinese.

Read a free Waymo lesson firstAlready a member? Sign in