Practice: Network Delay Time

Problem: https://leetcode.com/problems/network-delay-time/

Recognition reminder: a signal starts at one node and travels along directed edges that each take some non-negative time. You want the moment the signal has reached every node, which is the time it reaches the node that is hardest (slowest) to reach. That is a single-source shortest-path question with non-negative weights: compute the shortest time from the source to each node, then take the largest of those times. If any node is never reached, the network never fully receives the signal.

Before you start (the five-beat rhythm)

  1. Your Pattern Card for this week is already written.
  2. Name the pattern aloud and write your approach as a plain-English comment before any code.
  3. Struggle floor: 25 minutes unaided. No hints, no AI, no Discuss tab.
  4. If stuck past the floor, ask the tutor for a hint. Six rungs, one per ask.
  5. Debrief in your commit message before moving to the next problem.

Your target

Fill these in yourself before you look at anyone else’s solution:

Target time complexity:  ____
Target space complexity: ____

The weights are non-negative, which should point you at one specific algorithm and its complexity in terms of edges and vertices. Note also what your answer should be when some node is unreachable.

Where your code goes

Write your solution in your own work repo (see getting-started.md), not in this folder. This folder ships only the problem spec and a provided-example test (tests/test_provided.py) so you can check the given cases locally before you submit to LeetCode’s judge. The judge is the oracle; the tutor will not confirm your answer by reading it.

Debrief (paste into your commit message) 

1. What pattern did this turn out to be?
2. What was the trigger phrase or input shape that should have made me reach for it?
3. What was the time and space complexity, and what would dominate at scale?
4. What edge case would have broken my first attempt?
5. What would I do differently in three days when I see this cold?