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HomeLeetCode ProblemsNumber of Ways to Assign Edge Weights II
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Hard#3559
LeetCode Problem

Number of Ways to Assign Edge Weights II

There is an undirected tree with n nodes labeled from 1 to n, rooted at node 1. The tree is represented by a 2D integer array edges of length n - 1, where edges[i] = [ui, vi] indicates that there is an edge between nodes ui and vi. Initially, all edges have a weight of 0. You must assign each edge a weight of either 1 or 2. The cost of a path between any two nodes u and v is the total weight of all edges in the path connecting them. You are given a 2D integer array queries. For each queries[i] = [ui, vi], determine the number of ways to assign weights to edges in the path such that the cost of the path between ui and vi is odd. Return an array answer, where answer[i] is the number of valid assignments for queries[i]. Since the answer may be large, apply modulo 109 + 7 to each answer[i]. Note: For each query, disregard all edges not in the path between node ui and vi.

ArrayMathDynamic ProgrammingTreeDepth-First Search

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Problem Breakdown

Understanding the Number of Ways to Assign Edge Weights II Problem

Let's break down this LeetCode problem and understand what makes it challenging in interview settings.

Problem Statement

There is an undirected tree with n nodes labeled from 1 to n, rooted at node 1. The tree is represented by a 2D integer array edges of length n - 1, where edges[i] = [ui, vi] indicates that there is an edge between nodes ui and vi. Initially, all edges have a weight of 0. You must assign each edge a weight of either 1 or 2. The cost of a path between any two nodes u and v is the total weight of all edges in the path connecting them. You are given a 2D integer array queries. For each queries[i] = [ui, vi], determine the number of ways to assign weights to edges in the path such that the cost of the path between ui and vi is odd. Return an array answer, where answer[i] is the number of valid assignments for queries[i]. Since the answer may be large, apply modulo 109 + 7 to each answer[i]. Note: For each query, disregard all edges not in the path between node ui and vi.

HardProblem #3559
LeetCode

Number of Ways to Assign Edge Weights II

Related Topics

ArrayMathDynamic ProgrammingTreeDepth-First Search

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Get real-time assistance for Number of Ways to Assign Edge Weights II problems during coding interviews. Phantom Code AI provides instant solutions and explanations.

Examples

# Example 1

Input
edges = [[1,2]], queries = [[1,1],[1,2]]
Output
[0,1]

# Example 2

Input
edges = [[1,2],[1,3],[3,4],[3,5]], queries = [[1,4],[3,4],[2,5]]
Output
[2,1,4]

Constraints

2 <= n <= 105
edges.length == n - 1
edges[i] == [ui, vi]
1 <= queries.length <= 105
queries[i] == [ui, vi]
1 <= ui, vi <= n
edges represents a valid tree.

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Solve Number of Ways to Assign Edge Weights II — There is an undirected tree with n nodes labeled from 1 to n, rooted at node 1. ...

Here's the optimal approach using Array:

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 Number of Ways to Assign Edge Weights II and using Phantom Code AI during coding interviews.

How does Phantom Code AI help me solve coding problems like Number of Ways to Assign Edge Weights II during interviews?
Phantom Code AI 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 Number of Ways to Assign Edge Weights II?
Phantom Code AI 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 AI help me communicate my solution for problems like Number of Ways to Assign Edge Weights II?
Yes. Phantom Code AI 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 AI assist with different programming languages for Number of Ways to Assign Edge Weights II type problems?
Phantom Code AI 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 AI help me avoid during Number of Ways to Assign Edge Weights II interviews?
Phantom Code AI 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 AI detectable when solving problems like Number of Ways to Assign Edge Weights II during live interviews?
No. Phantom Code AI 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 AI help when I'm struggling with Number of Ways to Assign Edge Weights II 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 AI work for the coding platforms used in Number of Ways to Assign Edge Weights II interviews?
Yes. Phantom Code AI works with all major coding platforms including LeetCode, HackerRank, CodeSignal, CoderPad, HackerEarth, and any browser-based coding environment.
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