#0254

Network Delay Time

MediumDSA28 min20 XP

Problem

Given directed edges [u, v, w], n nodes labeled 1 to n, and source k, return the time for all nodes to receive the signal, or -1 if some node is unreachable.

Why This Matters

Dijkstra is the default shortest-path tool when edges have non-negative weights.

Function Signature

def network_delay_time(times, n, k):

Examples

Example 1

Inputtimes = [[2,1,1],[2,3,1],[3,4,1]], n = 4, k = 2

Output2

Node 4 receives the signal after 2 total time through 2 -> 3 -> 4.

Constraints

Return the exact requested value.
Handle empty or small inputs when the prompt allows them.
Prefer the target DSA pattern over brute force when the input can grow.

CodePython

def network_delay_time(times, n, k):
    """
    Input example: times = [[2,1,1],[2,3,1],[3,4,1]], n = 4, k = 2
    Return: 2
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return -1

def network_delay_time(times, n, k):
    """
    Input example: times = [[2,1,1],[2,3,1],[3,4,1]], n = 4, k = 2
    Return: 2
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return -1

Visible browser tests run here when available.

Testcases2 visible / 3 hidden categories

Reachable graph

Inputsource 2

Expected2

The farthest shortest distance is 2.

Unreachable node

Inputn = 2, edge 1 -> 2, source 2

Expected-1

Node 1 cannot be reached from node 2.

Hidden Test Categories

multiple edges from same nodesingle node graphlonger indirect path beats direct path