Is Count Symmetric Integers easy or hard?

Count Symmetric Integers is categorized as an Easy problem. The logic relies on simple digit manipulation and range iteration, making it a good exercise for beginners practicing math-based enumeration problems.

Count Symmetric Integers Python/Java solution

Python and Java implementations both iterate through the range and check digit symmetry. Python often uses string slicing for simplicity, while Java commonly extracts digits with division and modulo. Both versions run in O(n) time and constant space.

How to solve Count Symmetric Integers in O(n)?

Iterate through the range and skip numbers with odd digit counts. For valid numbers, extract digits using arithmetic operations like modulo and division. Compare the sum of the first half of digits with the second half. Each number is processed in constant time, giving O(n) overall complexity.

What is the best approach for Count Symmetric Integers?

Digit analysis is the best approach. Iterate from low to high and check only numbers with an even digit count. Extract digits using division and modulo, then compare the sum of the first half and second half. This runs in O(n) time and O(1) space.

Is Count Symmetric Integers asked at Google/Amazon/Meta?

This problem represents a common interview pattern involving digit manipulation and enumeration. Variants of digit-sum checks and numeric property problems appear in interviews at companies like Amazon and Google to evaluate basic algorithmic reasoning.

What data structure is used in Count Symmetric Integers?

No complex data structures are required. The solution mainly uses integer arithmetic and basic loops. Some implementations convert numbers to strings, but the optimal approach relies on direct digit extraction using math operations.

What is the time complexity of Count Symmetric Integers?

The typical optimized solution runs in O(n) time where n is the size of the range (high - low + 1). Each number is checked with constant-time digit extraction. Space complexity remains O(1) since only a few variables are used.

Description Hints 2 Solution Video 18:58

2843. Count Symmetric Integers

Easy82.5% acceptance5 companies

You are given two positive integers low and high.

An integer x consisting of 2 * n digits is symmetric if the sum of the first n digits of x is equal to the sum of the last n digits of x. Numbers with an odd number of digits are never symmetric.

Return the number of symmetric integers in the range [low, high].

Example 1:

Input: low = 1, high = 100
Output: 9
Explanation: There are 9 symmetric integers between 1 and 100: 11, 22, 33, 44, 55, 66, 77, 88, and 99.

Example 2:

Input: low = 1200, high = 1230
Output: 4
Explanation: There are 4 symmetric integers between 1200 and 1230: 1203, 1212, 1221, and 1230.

Constraints:

1 <= low <= high <= 10⁴

Asked at 5 companies

Bloomberg

Google Amazon Microsoft Meta

Topics

Enumeration Math

Hints open one at a time

Hint 1

Iterate over all numbers from low to high

Hint 2

Convert each number to a string and compare the sum of the first half with that of the second.

18:58

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