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Grokking the Coding Interview Patterns in C++

Solution: Reorder Routes to Make All Paths Lead to the City Zero

Explore how to solve the problem of reorienting one-way roads in a tree structure so every city can reach city zero. This lesson explains building an adjacency list with direction flags and using depth-first search to count the minimum road reversals required. Understand the algorithm's efficiency in time and space while applying graph traversal techniques to solve a real-world inspired challenge.

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Statement

There are n cities labeled from 00 to n−1n - 1, connected by n−1n - 1 roads, so there is only one route between any two cities. This road network forms a tree structure.

Last year, the Ministry of transport made all roads one-way due to their narrow width. These roads are represented as connections, where each entry connections[i] =[ai,bi]= [a_i, b_i] means there is a road going from city aia_i to city bib_i ...