CodingMediumcod-g748

Subject GraphsLevel Mid–Senior~25 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

There are n cities (0..n-1) connected by n-1 one-way roads forming a tree if you ignore direction. City 0 is the capital. Each road is given as `[a, b]` meaning a directed road from a to b. You can reverse the direction of any road. Return the minimum number of roads you must reverse so that every city can reach the capital (city 0). 1 <= n.

Implement

min_reorder_to_capital(n: int, connections: list[list[int]]) → int

Examples

in[6,[[0,1],[1,3],[2,3],[4,0],[4,5]]]out3

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.