CodingMediumcod-g252

Subject Advanced graphsLevel Mid–Senior~30 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Given an unweighted undirected graph with n nodes (0..n-1) and edges [u, v], return the number of distinct shortest paths from a source to a destination, taken modulo 1000000007. If the destination is unreachable, return 0; if source equals destination, return 1. Constraints: 1 <= n <= 2000.

Implement

count_shortest_paths(n: int, edges: list[list[int]], src: int, dst: int) → int

Examples

in[4,[[0,1],[0,2],[1,3],[2,3]],0,3]out2

What a strong answer looks like

State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.

Learn the concepts

Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.

Run or narrate your approach, then ask the coach.