Leetcode #1440: Evaluate Boolean Expression
In this guide, we solve Leetcode #1440 Evaluate Boolean 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
Table Variables: +---------------+---------+ | Column Name | Type | +---------------+---------+ | name | varchar | | value | int | +---------------+---------+ In SQL, name is the primary key for this table. This table contains the stored variables and their values.
Quick Facts
- Difficulty: Medium
- Premium: Yes
- Tags: Database
Intuition
The task is relational in nature, which maps cleanly to DataFrame operations in Python.
By treating tables as DataFrames, joins and group-bys become concise and readable.
Approach
Load the inputs as DataFrames and apply the appropriate merge, filter, or group-by.
Select or rename the columns to match the required output.
Steps:
- Load inputs as DataFrames.
- Apply merge/groupby/filter operations.
- Select the output columns.
Example
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| name | varchar |
| value | int |
+---------------+---------+
In SQL, name is the primary key for this table.
This table contains the stored variables and their values.
Python Solution
import duckdb
import pandas as pd
# Pass input tables as keyword arguments matching the SQL table names.
def solution(**tables) -> pd.DataFrame:
con = duckdb.connect()
for name, df in tables.items():
con.register(name, df)
return con.execute("""SELECT
left_operand,
operator,
right_operand,
CASE
WHEN (
(operator = '=' AND v1.value = v2.value)
OR (operator = '>' AND v1.value > v2.value)
OR (operator = '<' AND v1.value < v2.value)
) THEN 'true'
ELSE 'false'
END AS value
FROM
Expressions AS e
JOIN Variables AS v1 ON e.left_operand = v1.name
JOIN Variables AS v2 ON e.right_operand = v2.name;""").df()
Complexity
The time complexity is O(n log n) (typical). 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.