Grokking Graph Algorithms for Coding Interviews
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Reorder Routes to Make All Paths Lead to the City Zero (medium)
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Problem Statement

You are given n cities labeled from 0 to n-1 and n-1 roads, which form a tree structure. Each road is directed, meaning it has a specific direction. These roads are represented by the array connections, where connections[i] = [a, b] indicates a road from city a to city b.

Change the direction of some roads so that every city can reach city 0.

Return the minimum number of edges that need to be reversed.

Examples

Example 1

  • Input: n = 5, connections = [[0, 1], [1, 2], [2, 3], [4, 3]]
  • Expected Output: 3

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