Network Delay Time 25 XP Medium

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Given a network of n nodes and weighted edges [u,v,w], find how long it takes for a signal from node k to reach all nodes. This is Dijkstra's algorithm — shortest path from a single source.

import heapq
# Dijkstra: min-heap of (distance, node)
# Greedily process nearest unvisited node
# Update neighbors if shorter path found

Answer = max of all shortest distances. If any node unreachable, return -1.

💡 Pro tip: Understand this problem deeply — don't just memorize the code. Try explaining the approach out loud as if teaching a friend. If you can explain it simply, you truly understand it!

📋 Instructions

Find network delay time using Dijkstra's algorithm.

Use heapq with (dist, node). Pop smallest, skip if visited. Update neighbors. Answer = max of all distances.

🧪 Test Cases

Input

networkDelayTime(times, 4, 2)

Expected

2

Test case 1

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main.py

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Output

Ready. Press ▶ Run or Ctrl+Enter.

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