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How to Solve Count Number of Possible Root Nodes Problem
Master the Count Number of Possible Root Nodes LeetCode problem with undetectable real-time assistance. Get instant solutions and explanations during your coding interviews.
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LeetCode ProblemCount Number of Possible Root Nodes
Alice has an undirected tree with n nodes labeled from 0 to n - 1. The tree is represented as a 2D integer array edges of length n - 1 where edges[i] = [ai, bi] indicates that there is an edge between nodes ai and bi in the tree. Alice wants Bob to find the root of the tree. She allows Bob to make several guesses about her tree. In one guess, he does the following: Bob's guesses are represented by a 2D integer array guesses where guesses[j] = [uj, vj] indicates Bob guessed uj to be the parent of vj. Alice being lazy, does not reply to each of Bob's guesses, but just says that at least k of his guesses are true. Given the 2D integer arrays edges, guesses and the integer k, return the number of possible nodes that can be the root of Alice's tree. If there is no such tree, return 0.
ArrayHash TableDynamic ProgrammingTreeDepth-First Search
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Problem Breakdown
Understanding the Count Number of Possible Root Nodes Problem
Let's break down this LeetCode problem and understand what makes it challenging in interview settings.
Problem Statement
Alice has an undirected tree with n nodes labeled from 0 to n - 1. The tree is represented as a 2D integer array edges of length n - 1 where edges[i] = [ai, bi] indicates that there is an edge between nodes ai and bi in the tree. Alice wants Bob to find the root of the tree. She allows Bob to make several guesses about her tree. In one guess, he does the following: Bob's guesses are represented by a 2D integer array guesses where guesses[j] = [uj, vj] indicates Bob guessed uj to be the parent of vj. Alice being lazy, does not reply to each of Bob's guesses, but just says that at least k of his guesses are true. Given the 2D integer arrays edges, guesses and the integer k, return the number of possible nodes that can be the root of Alice's tree. If there is no such tree, return 0.
HardProblem #2581
LeetCodeCount Number of Possible Root Nodes
Related Topics
ArrayHash TableDynamic ProgrammingTreeDepth-First Search
How Phantom Code Helps
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Examples
# Example 1
Input
edges = [[0,1],[1,2],[1,3],[4,2]], guesses = [[1,3],[0,1],[1,0],[2,4]], k = 3
Output
3
# Example 2
Input
edges = [[0,1],[1,2],[2,3],[3,4]], guesses = [[1,0],[3,4],[2,1],[3,2]], k = 1
Output
5
Constraints
edges.length == n - 1
2 <= n <= 105
1 <= guesses.length <= 105
0 <= ai, bi, uj, vj <= n - 1
ai != bi
uj != vj
edges represents a valid tree.
guesses[j] is an edge of the tree.
guesses is unique.
0 <= k <= guesses.length
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Solve Count Number of Possible Root Nodes — Alice has an undirected tree with n nodes labeled from 0 to n - 1. The tree is r...
Here's the optimal approach using Array:
def solve(input):
# Optimal O(n) solution
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Time: O(n) | Space: O(n)
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Frequently Asked Questions
Common questions about solving Count Number of Possible Root Nodes and using Phantom Code during coding interviews.
How does Phantom Code help me solve coding problems like Count Number of Possible Root Nodes 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 Count Number of Possible Root Nodes?
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 Count Number of Possible Root Nodes?
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 Count Number of Possible Root Nodes 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 Count Number of Possible Root Nodes 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 Count Number of Possible Root Nodes during live interviews?
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How does Phantom Code help when I'm struggling with Count Number of Possible Root Nodes 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 Count Number of Possible Root Nodes 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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