Leetcode #2756: Query Batching
In this guide, we solve Leetcode #2756 Query Batching 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
Batching multiple small queries into a single large query can be a useful optimization. Write a class QueryBatcher that implements this functionality.
Quick Facts
- Difficulty: Hard
- Premium: Yes
- Tags: JavaScript
Intuition
The constraints allow a direct scan that keeps only the essential state.
By translating the requirements into a clean loop, the logic stays easy to reason about.
Approach
Iterate through the data once, updating the state needed to compute the answer.
Return the final state after the traversal is complete.
Steps:
- Parse the input.
- Iterate and update state.
- Return the computed answer.
Example
Input:
queryMultiple = async function(keys) {
return keys.map(key => key + '!');
}
t = 100
calls = [
{"key": "a", "time": 10},
{"key": "b", "time": 20},
{"key": "c", "time": 30}
]
Output: [
{"resolved": "a!", "time": 10},
{"resolved": "b!", "time": 110},
{"resolved": "c!", "time": 110}
]
Explanation:
const batcher = new QueryBatcher(queryMultiple, 100);
setTimeout(() => batcher.getValue('a'), 10); // "a!" at t=10ms
setTimeout(() => batcher.getValue('b'), 20); // "b!" at t=110ms
setTimeout(() => batcher.getValue('c'), 30); // "c!" at t=110ms
queryMultiple simply adds an "!" to the key
At t=10ms, getValue('a') is called, queryMultiple(['a']) is immediately called and the result is immediately returned.
At t=20ms, getValue('b') is called but the query is queued
At t=30ms, getValue('c') is called but the query is queued.
At t=110ms, queryMultiple(['a', 'b']) is called and the results are immediately returned.
Python Solution
# TODO: add Python solution
Complexity
The time complexity is O(n). The space complexity is O(1) to 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.