← 返回博客列表
VO TikTok

[TikTok Interview Question] Division Equation LeetCode 399: Why Does This Simple Graph Theory Problem Filter Out 70% of Candidates?

2025-08-12

TikTok Division Equation Interview

Recently in our oavoservice interview assistance services, TikTok interviews have frequently featured a classic "division equation" problem — LeetCode 399.

The problem seems simple but hides subtle traps. Many candidates think at first glance: "This is just mathematical computation, right?" Wrong. This problem tests graph theory modeling ability and DFS traversal techniques, and 90% of mathematical approaches will crash during Follow-up questions.

Let's see how oavoservice real-time interview assistance helps candidates identify the interviewer's traps.

01 TikTok Interview Original Question (Complete English Version)

Title: Division

You are given an array of variable pairs equations and an array of real numbers values, where equations[i] = [Ai, Bi] and values[i] represent the equation Ai / Bi = values[i].

Each Ai or Bi is a string that represents a single variable.

You are also given some queries, where queries[j] = [Cj, Dj] represents the jth query where you must find the answer for Cj / Dj = ?. Return the answers to all queries. If a single answer cannot be determined, return -1.0.

Note:

Example Input:

equations = [["a","b"],["b","c"]]
values = [2.0,3.0]
queries = [["a","c"],["b","a"],["a","e"],["a","a"],["x","x"]]

Output: [6.00000,0.50000,-1.00000,1.00000,-1.00000]

02 Common Candidate Mistake: Falling into "Mathematical Computation" Mindset

Most candidates see this problem and their first reaction is:

"I need to solve this using algebraic equation systems, build matrices, then use Gaussian elimination..."

Stop! The interviewer thinks: "Another programmer brainwashed by math class."

This approach might work for simple cases, but when the interviewer asks:

The mathematical approach instantly crashes with exploding time complexity.

03 oavoservice Key Guidance: Graph Theory Modeling Approach

In our real-time assistance, we quickly point candidates in the right direction:

Core Insight: Treat variables as nodes and division relationships as directed weighted edges!

One-sentence solution:

Treat variables as nodes, division as directed weighted edges, use DFS to find paths and multiply weights.

04 oavoservice Optimized Solution (Live Implementation)

from collections import defaultdict

def calcEquation(equations, values, queries):
    # 1. Build graph: g[X][Y] = value of X/Y; also build reverse edge g[Y][X] = 1/value
    graph = defaultdict(dict)
    for (x, y), val in zip(equations, values):
        graph[x][y] = val
        graph[y][x] = 1.0 / val
    
    # 2. DFS: from start to end, multiply weights along the way
    def dfs(start, end, visited):
        # Handle boundary cases
        if start not in graph or end not in graph:
            return -1.0
        if start == end:
            return 1.0
        
        visited.add(start)
        for neighbor, weight in graph[start].items():
            if neighbor in visited:
                continue
            result = dfs(neighbor, end, visited)
            if result != -1.0:
                return weight * result
        return -1.0
    
    # 3. Process all queries
    return [dfs(c, d, set()) for c, d in queries]

# Verify results
equations = [["a","b"],["b","c"]]
values = [2.0, 3.0]
queries = [["a","c"],["b","a"],["a","e"],["a","a"],["x","x"]]
print(calcEquation(equations, values, queries))
# Output: [6.0, 0.5, -1.0, 1.0, -1.0]

05 Interviewer Follow-ups & Optimization Points

After candidates write the basic version, TikTok interviewers typically ask:

Q1: "How can you optimize time complexity?"

oavoservice guidance approach:

Q2: "If there are many queries, how would you preprocess?"

Advanced solution: Floyd-Warshall all-pairs shortest path

# Preprocessing: O(V³) to calculate paths between any two nodes
def preprocess_all_paths(graph):
    nodes = list(graph.keys())
    for k in nodes:
        for i in nodes:
            for j in nodes:
                if k in graph[i] and j in graph[k]:
                    graph[i][j] = graph[i][k] * graph[k][j]

Q3: "Does it support dynamic updates?"

Real-time update strategy:

06 Why Do 70% of Candidates Fail?

  1. Wrong approach: Obsessing over mathematical formulas, ignoring graph theory essence
  2. Missing boundaries: Forgetting to handle x/x = 1 and undefined variables -1
  3. No cycle detection: DFS without visited set leads to infinite loops
  4. Poor complexity awareness: Unable to optimize for large datasets

What interviewers really want to see: The ability to abstract real-world problems into graph theory models.

🚀 oavoservice TikTok Interview Professional Assistance

As one of the most active companies for 2025 summer recruitment, TikTok's interview difficulty and competition level are rising. If you received a TikTok interview invitation but worry about:

❌ Unclear graph theory modeling approaches
❌ Weak grasp of DFS/BFS algorithms
❌ Unable to quickly optimize during interviewer follow-ups
❌ Lack of big tech interview experience and techniques

oavoservice professional interview assistance team will support you!

Our TikTok Specialized Services:

✅ Real-time Interview Assistance - Provide guidance at critical moments
✅ Algorithm Intensive Training - Graph theory, dynamic programming, system design expertise
✅ TikTok Question Bank - Latest interview questions and standard solutions
✅ Mock Interview Training - 1-on-1 realistic interview simulations

📊 2025 Summer Recruitment Data:

📱 Get TikTok Interview Questions Now

WeChat: Coding0201

🎯 Limited Time Offer: Add WeChat for free:

oavoservice - Make every interview your home court!

Keywords: TikTok interview, LeetCode 399, division equation, graph theory algorithm, DFS traversal, interview assistance, interview help, interview cheating, VO assistance, algorithm interview, summer internship, North America job search, oavoservice