Leetcode #2443: Sum of Number and Its Reverse
In this guide, we solve Leetcode #2443 Sum of Number and Its Reverse 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
Given a non-negative integer num, return true if num can be expressed as the sum of any non-negative integer and its reverse, or false otherwise. Example 1: Input: num = 443 Output: true Explanation: 172 + 271 = 443 so we return true.
Quick Facts
- Difficulty: Medium
- Premium: No
- Tags: Math, Enumeration
Intuition
There is a mathematical invariant or formula that directly leads to the result.
Using math avoids unnecessary loops and reduces complexity.
Approach
Derive the formula or update rule, then compute the answer directly.
Handle edge cases like overflow or zero carefully.
Steps:
- Identify the math relationship.
- Compute the result with a loop or formula.
- Handle edge cases.
Example
Input: num = 443
Output: true
Explanation: 172 + 271 = 443 so we return true.
Python Solution
class Solution:
def sumOfNumberAndReverse(self, num: int) -> bool:
return any(k + int(str(k)[::-1]) == num for k in range(num + 1))
Complexity
The time complexity is , where is the size of . The space complexity is O(1).
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.