Depth-First Search Questions at ServiceNow: What to Expect

Depth-First Search (DFS) is a fundamental algorithm for exploring graphs and trees, making it essential for solving problems involving hierarchical data, dependency resolution, and pathfinding. At ServiceNow, a platform built on managing complex IT workflows and service dependencies, these scenarios are common. The company's technical interviews include DFS to assess your ability to navigate and manipulate interconnected data structures, which directly mirrors real-world tasks like traversing configuration item relationships, parsing workflow logic, or analyzing organizational hierarchies. With DFS appearing in approximately 9% of their tagged problems, demonstrating proficiency is a practical necessity.

What to Expect — Types of Problems

ServiceNow’s DFS questions typically focus on applied scenarios rather than abstract algorithmic puzzles. You can expect problems centered on tree and graph traversal within a business or systems context.

• Tree Traversal & Modification: Questions often involve Company Hierarchy trees or Category Trees (like those for IT services). Tasks may include finding a specific node, calculating aggregated metrics across subtrees, or pruning sections of a tree based on a condition.
• Pathfinding in Graphs: While less frequent than pure tree problems, you might encounter scenarios requiring path exploration, such as checking dependencies between system components or determining if a sequence of approvals is valid. These problems test your ability to handle cycles and avoid repeated visits.
• Combination with Other Concepts: DFS is rarely tested in isolation. Be prepared to combine it with core data structures like HashMaps (for memoization or tracking visited nodes) or integrate it with string processing and object-oriented design relevant to ServiceNow’s platform data models.

How to Prepare — Study Tips with One Code Example

Master the recursive and iterative (stack-based) implementations of DFS. For interviews, the recursive approach is often clearer for tree problems, while the iterative method is safer for deep graphs to avoid stack overflow. Practice identifying the base case and the recursive traversal logic. A key pattern is performing an action in a pre-order, in-order (for binary trees), or post-order sequence depending on whether you need to process a node before exploring its children, between them, or after.

A common task is searching for a target value in a generic tree (N-ary tree). Here is the standard DFS pattern applied to this problem.

class TreeNode:
    def __init__(self, val=0, children=None):
        self.val = val
        self.children = children if children is not None else []

def dfs_find(root, target):
    if not root:
        return False
    if root.val == target:  # Pre-order check
        return True
    for child in root.children:
        if dfs_find(child, target):
            return True
    return False

Recommended Practice Order

Build your skills progressively. Start with basic binary tree traversals (pre-order, in-order, post-order) to internalize the recursion pattern. Move on to standard N-ary tree problems, like finding a node or calculating maximum depth. Then, tackle graph traversal problems on small grids or adjacency lists, ensuring you implement a visited set to prevent infinite loops. Finally, practice ServiceNow-specific problems that layer in business logic, such as filtering a hierarchy of configuration items or summing values in a subtree based on a condition. This sequence solidifies the core algorithm before adding domain complexity.

Practice Depth-First Search at ServiceNow