Leetcode #2979: Most Expensive Item That Can Not Be Bought
In this guide, we solve Leetcode #2979 Most Expensive Item That Can Not Be Bought 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 two distinct prime numbers primeOne and primeTwo. Alice and Bob are visiting a market.
Quick Facts
- Difficulty: Medium
- Premium: Yes
- Tags: Math, Dynamic Programming, Number Theory
Intuition
The problem breaks into overlapping subproblems, so caching results prevents exponential repetition.
A carefully chosen DP state captures exactly what we need to build the final answer.
Approach
Define the DP state and recurrence, then compute states in the correct order.
Optionally compress space once the recurrence is clear.
Steps:
- Choose a DP state definition.
- Write the recurrence and base cases.
- Compute states in the correct order.
Example
Input: primeOne = 2, primeTwo = 5
Output: 3
Explanation: The prices of items which cannot be bought are [1,3]. It can be shown that all items with a price greater than 3 can be bought using a combination of coins of denominations 2 and 5.
Python Solution
class Solution:
def mostExpensiveItem(self, primeOne: int, primeTwo: int) -> int:
return primeOne * primeTwo - primeOne - primeTwo
Complexity
The time complexity is , and the space complexity is . 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.