Find Each Cell's Nearest Source
Company: DoorDash
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Onsite
Given an `m x n` grid containing `1` for source cells and `0` for regular cells, compute for every cell the shortest 4-directional distance to any source cell. Moving up, down, left, or right costs 1 step. Return an `m x n` matrix of distances, where every source cell has distance `0`. If the grid contains no source cells, return `-1` for every cell.
Quick Answer: This question evaluates understanding of shortest-path computation and distance labeling in grid-based graphs, measuring competency in algorithmic problem solving and efficient traversal strategies.