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How to Solve Reorder Routes to Make All Paths Lead to the City Zero Problem
Master the Reorder Routes to Make All Paths Lead to the City Zero LeetCode problem with undetectable real-time assistance. Get instant solutions and explanations during your coding interviews.
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Start Free for WindowsMedium#1466
LeetCode ProblemReorder Routes to Make All Paths Lead to the City Zero
There are n cities numbered from 0 to n - 1 and n - 1 roads such that there is only one way to travel between two different cities (this network form a tree). Last year, The ministry of transport decided to orient the roads in one direction because they are too narrow. Roads are represented by connections where connections[i] = [ai, bi] represents a road from city ai to city bi. This year, there will be a big event in the capital (city 0), and many people want to travel to this city. Your task consists of reorienting some roads such that each city can visit the city 0. Return the minimum number of edges changed. It's guaranteed that each city can reach city 0 after reorder.
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Problem Breakdown
Understanding the Reorder Routes to Make All Paths Lead to the City Zero Problem
Let's break down this LeetCode problem and understand what makes it challenging in interview settings.
Problem Statement
There are n cities numbered from 0 to n - 1 and n - 1 roads such that there is only one way to travel between two different cities (this network form a tree). Last year, The ministry of transport decided to orient the roads in one direction because they are too narrow. Roads are represented by connections where connections[i] = [ai, bi] represents a road from city ai to city bi. This year, there will be a big event in the capital (city 0), and many people want to travel to this city. Your task consists of reorienting some roads such that each city can visit the city 0. Return the minimum number of edges changed. It's guaranteed that each city can reach city 0 after reorder.
MediumProblem #1466
LeetCodeReorder Routes to Make All Paths Lead to the City Zero
Related Topics
Depth-First SearchBreadth-First SearchGraph
How Phantom Code Helps
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Examples
# Example 1
Input
n = 6, connections = [[0,1],[1,3],[2,3],[4,0],[4,5]]
Output
3
# Example 2
Input
n = 5, connections = [[1,0],[1,2],[3,2],[3,4]]
Output
2
# Example 3
Input
n = 3, connections = [[1,0],[2,0]]
Output
0
Constraints
2 <= n <= 5 * 104
connections.length == n - 1
connections[i].length == 2
0 <= ai, bi <= n - 1
ai != bi
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Solve Reorder Routes to Make All Paths Lead to the City Zero — There are n cities numbered from 0 to n - 1 and n - 1 roads such that there is o...
Here's the optimal approach using Depth-First Search:
def solve(input):
# Optimal O(n) solution
return result
Time: O(n) | Space: O(n)
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Frequently Asked Questions
Common questions about solving Reorder Routes to Make All Paths Lead to the City Zero and using Phantom Code during coding interviews.
How does Phantom Code help me solve coding problems like Reorder Routes to Make All Paths Lead to the City Zero during interviews?
Phantom Code generates complete solutions instantly with proper complexity analysis, letting you focus on explaining your approach and demonstrating problem-solving skills rather than getting stuck on implementation details during high-pressure situations.
What if the interviewer asks follow-up questions or modifications to problems like Reorder Routes to Make All Paths Lead to the City Zero?
Phantom Code adapts in real-time. Screenshot the modified problem or use audio mode to capture the interviewer's follow-up, and get an updated solution within seconds — including edge cases and optimizations.
Can Phantom Code help me communicate my solution for problems like Reorder Routes to Make All Paths Lead to the City Zero?
Yes. Phantom Code provides step-by-step approach explanations with 3 progressive thoughts, so you can walk through your solution naturally. It also provides time and space complexity analysis to discuss trade-offs.
How does Phantom Code assist with different programming languages for Reorder Routes to Make All Paths Lead to the City Zero type problems?
Phantom Code supports 11 programming languages including Python, Java, C++, JavaScript, TypeScript, Go, Rust, Ruby, Swift, Kotlin, and C#. Set your preferred language and get idiomatic solutions.
What coding mistakes does Phantom Code help me avoid during Reorder Routes to Make All Paths Lead to the City Zero interviews?
Phantom Code catches common mistakes like off-by-one errors, missing edge cases, incorrect base conditions, and suboptimal approaches. It provides clean, well-structured code that handles all edge cases.
Is Phantom Code detectable when solving problems like Reorder Routes to Make All Paths Lead to the City Zero during live interviews?
No. Phantom Code runs as an invisible desktop overlay that doesn't appear in screen shares, recordings, or proctoring software. It works with Zoom, HackerRank, CodeSignal, CoderPad, and all major platforms.
How does Phantom Code help when I'm struggling with Reorder Routes to Make All Paths Lead to the City Zero style questions under pressure?
The AI provides structured guidance: first the approach (what algorithm/data structure to use and why), then the implementation with clean code, and finally complexity analysis. This helps you think clearly even under pressure.
Does Phantom Code work for the coding platforms used in Reorder Routes to Make All Paths Lead to the City Zero interviews?
Yes. Phantom Code works with all major coding platforms including LeetCode, HackerRank, CodeSignal, CoderPad, HackerEarth, and any browser-based coding environment.
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