Leetcode #1739: Building Boxes
In this guide, we solve Leetcode #1739 Building Boxes 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 have a cubic storeroom where the width, length, and height of the room are all equal to n units. You are asked to place n boxes in this room where each box is a cube of unit side length.
Quick Facts
- Difficulty: Hard
- Premium: No
- Tags: Greedy, Math, Binary Search
Intuition
The problem structure suggests a monotonic decision, which makes binary search a natural fit.
By halving the search space each step, we reach the answer efficiently.
Approach
Search either directly on a sorted array or on the answer space using a check function.
Each check is fast, and the logarithmic search keeps the overall runtime low.
Steps:
- Define the search bounds.
- Check the mid point condition.
- Narrow the bounds until convergence.
Example
Input: n = 3
Output: 3
Explanation: The figure above is for the placement of the three boxes.
These boxes are placed in the corner of the room, where the corner is on the left side.
Python Solution
class Solution:
def minimumBoxes(self, n: int) -> int:
s, k = 0, 1
while s + k * (k + 1) // 2 <= n:
s += k * (k + 1) // 2
k += 1
k -= 1
ans = k * (k + 1) // 2
k = 1
while s < n:
ans += 1
s += k
k += 1
return ans
Complexity
The time complexity is , where is the number of boxes given in the problem. 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.