Method Chaining - Video Solutions

Problem Overview: The task models a sequence of operations that behave like chained method calls. Each step depends on the previous result, so you must process the operations in order and maintain the current state correctly while keeping the implementation efficient.

Approach 1: Using a HashMap or Dictionary (O(n) time, O(n) space)

This approach stores intermediate state or operation mappings in a HashMap (or dictionary). As you iterate through the sequence, each operation updates the current state using constant-time hash lookups. The key idea is that a map lets you quickly retrieve or update values associated with specific method names or identifiers without scanning the entire structure. This approach works well when the problem involves tracking values, resolving repeated operations, or aggregating results across the chain. Hash lookups keep updates at O(1) on average, leading to an overall O(n) traversal of the operations.

Hash maps are a common tool for problems that require quick lookups or state tracking. If you're reviewing related patterns, see hash map techniques frequently used in many array and string problems.

Approach 2: Two-Pointer Technique (O(n) time, O(1) space)

The two-pointer technique processes the chain from both ends of the sequence. One pointer starts at the beginning while the other starts at the end, and both move inward depending on how operations interact. This works particularly well when opposite operations can cancel out or when evaluating the chain requires comparing elements from both sides. Because you only maintain a few indices and update them as you scan, the extra memory usage stays constant.

This method avoids the overhead of additional data structures and is often faster in practice due to better cache locality. It is a standard pattern in problems involving ordered data or symmetric processing. If you want more practice with this pattern, review two pointer problems and related array traversal strategies.

Recommended for interviews: Start with the HashMap-based solution to show you understand how to manage state and perform constant-time lookups during the chain evaluation. Then discuss the two-pointer optimization if the operations allow symmetric processing. Interviewers typically prefer the O(n) time, O(1) space two-pointer approach when applicable because it demonstrates stronger algorithmic reasoning and space optimization.