Leetcode #2412: Minimum Money Required Before Transactions
In this guide, we solve Leetcode #2412 Minimum Money Required Before Transactions 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
You are given a 0-indexed 2D integer array transactions, where transactions[i] = [costi, cashbacki]. The array describes transactions, where each transaction must be completed exactly once in some order.
Quick Facts
- Difficulty: Hard
- Premium: No
- Tags: Greedy, Array, Sorting
Intuition
A locally optimal choice leads to a globally optimal result for this structure.
That means we can commit to decisions as we scan without backtracking.
Approach
Sort or preprocess if needed, then repeatedly take the best available local choice.
Maintain the minimal state necessary to validate the greedy decision.
Steps:
- Sort or preprocess as needed.
- Iterate and pick the best local option.
- Track the current solution.
Example
Input: transactions = [[2,1],[5,0],[4,2]]
Output: 10
Explanation:
Starting with money = 10, the transactions can be performed in any order.
It can be shown that starting with money < 10 will fail to complete all transactions in some order.
Python Solution
class Solution:
def minimumMoney(self, transactions: List[List[int]]) -> int:
s = sum(max(0, a - b) for a, b in transactions)
ans = 0
for a, b in transactions:
if a > b:
ans = max(ans, s + b)
else:
ans = max(ans, s + a)
return ans
Complexity
The time complexity is , where is the number of transactions. The space complexity is .
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.