Leetcode #1597: Build Binary Expression Tree From Infix Expression
In this guide, we solve Leetcode #1597 Build Binary Expression Tree From Infix Expression in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
A binary expression tree is a kind of binary tree used to represent arithmetic expressions. Each node of a binary expression tree has either zero or two children.
Quick Facts
- Difficulty: Hard
- Premium: Yes
- Tags: Stack, Tree, String, Binary Tree
Intuition
The problem has a natural nested or last-in-first-out structure.
A stack lets us resolve matches in the correct order as we scan.
Approach
Push items as they appear and pop when you can finalize a decision.
The stack captures the unresolved part of the input.
Steps:
- Push elements as you scan.
- Pop when a rule or match is satisfied.
- Use the stack to compute results.
Example
Input: s = "3*4-2*5"
Output: [-,*,*,3,4,2,5]
Explanation: The tree above is the only valid tree whose inorder traversal produces s.
Python Solution
Complexity
The time complexity is O(n). The space complexity is O(n).
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.