Is Sum of Number and Its Reverse easy or hard?

The problem is rated Medium on LeetCode because it requires recognizing that the search space is bounded and implementing digit reversal correctly. The logic itself is straightforward once you realize you can simply enumerate possible values.

Sum of Number and Its Reverse Python/Java solution

In Python or Java, iterate from 0 to num, compute the reversed number using a loop that extracts digits, and check whether x + reversed equals num. If a match is found, return true; otherwise continue until the range is exhausted. The implementation uses constant extra space.

How to solve Sum of Number and Its Reverse in O(n)?

Iterate through numbers from 0 to num and compute the reversed digits for each candidate. For each value x, calculate reverse(x) using repeated modulus and division operations, then check whether x + reverse(x) equals num. The loop runs n times, and digit reversal adds a logarithmic factor, giving O(n log n) time overall.

What is the best approach for Sum of Number and Its Reverse?

The standard solution is enumeration. Iterate through every integer x from 0 to num, compute reverse(x), and check if x + reverse(x) equals num. This runs in O(n log n) time because reversing digits takes O(log n) per iteration and uses O(1) extra space.

Is Sum of Number and Its Reverse asked at Google/Amazon/Meta?

This problem represents the type of math and enumeration question commonly used in technical screens. Variations involving digit manipulation or reversing numbers appear in interviews at companies like Google, Amazon, and Meta to test reasoning with numeric transformations.

What data structure is used in Sum of Number and Its Reverse?

No specialized data structure is required. The solution relies on simple integer arithmetic and digit manipulation. Enumeration and mathematical operations are the primary techniques used.

What is the time complexity of Sum of Number and Its Reverse?

The typical solution runs in O(n log n) time. You may test up to n candidates, and reversing the digits of each number costs O(log n) based on the number of digits. Space complexity remains O(1) because only a few variables are used during computation.

Description Hints 2 Solution Video 3:42

2443. Sum of Number and Its Reverse

Medium50.0% acceptance1 company

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.

Example 2:

Input: num = 63
Output: false
Explanation: 63 cannot be expressed as the sum of a non-negative integer and its reverse so we return false.

Example 3:

Input: num = 181
Output: true
Explanation: 140 + 041 = 181 so we return true. Note that when a number is reversed, there may be leading zeros.

Constraints:

0 <= num <= 10⁵

Asked at 1 company

Amazon

Topics

Enumeration Math

Hints open one at a time

Hint 1

The constraints are small enough that we can check every number.

Hint 2

To reverse a number, first convert it to a string. Then, create a new string that is the reverse of the first one. Finally, convert the new string back into a number.

3:42

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