Is Confusing Number easy or hard?

Confusing Number is classified as an Easy problem on LeetCode with an acceptance rate around 49%. The challenge mainly involves recognizing valid digit rotations and constructing the rotated number correctly.

Confusing Number Python/Java solution

Implement a mapping for valid rotations and iterate through the digits using modulo and division. Build the rotated number and compare it with the original. The same logic works across Python, Java, C++, Go, and PHP with O(d) time and constant extra space.

How to solve Confusing Number in O(n)?

Treat n as the number of digits. Iterate through the digits from right to left, map each digit to its rotated equivalent, and construct the new number. If any digit is invalid (2,3,4,5,7), return false. After building the rotated value, check if it differs from the original number.

What is the best approach for Confusing Number?

The best approach rotates digits using arithmetic operations and a mapping of valid rotations (0→0, 1→1, 6→9, 8→8, 9→6). Extract digits with modulo, build the rotated number in reverse order, and compare it with the original. This runs in O(d) time with O(1) space where d is the number of digits.

Is Confusing Number asked at Google/Amazon/Meta?

Confusing Number appears in interview preparation sets related to number manipulation and digit transformations. Variants such as Confusing Number II are more frequently reported in big tech interview discussions, especially for companies like Google and Amazon.

What data structure is used in Confusing Number?

Most solutions use a small constant mapping structure that maps digits to their rotated equivalents. This can be implemented with a hash map, array, or switch statement since there are only five valid digits (0,1,6,8,9).

What is the time complexity of Confusing Number?

The time complexity is O(d) because each digit of the number is processed once. The algorithm extracts digits using modulo and division operations and constructs the rotated value step by step. Space complexity can be O(1) when using pure arithmetic.

Description Hints 1 Solution Video 15:41

1056. Confusing Number

Easy49.8% acceptance1 companyPremium elsewhere, free here

A confusing number is a number that when rotated 180 degrees becomes a different number with each digit valid.

We can rotate digits of a number by 180 degrees to form new digits.

When 0, 1, 6, 8, and 9 are rotated 180 degrees, they become 0, 1, 9, 8, and 6 respectively.
When 2, 3, 4, 5, and 7 are rotated 180 degrees, they become invalid.

Note that after rotating a number, we can ignore leading zeros.

For example, after rotating 8000, we have 0008 which is considered as just 8.

Given an integer n, return true if it is a confusing number, or false otherwise.

Example 1:

Input: n = 6
Output: true
Explanation: We get 9 after rotating 6, 9 is a valid number, and 9 != 6.

Example 2:

Input: n = 89
Output: true
Explanation: We get 68 after rotating 89, 68 is a valid number and 68 != 89.

Example 3:

Input: n = 11
Output: false
Explanation: We get 11 after rotating 11, 11 is a valid number but the value remains the same, thus 11 is not a confusing number

Constraints:

0 <= n <= 10⁹

Asked at 1 company

Google

Topics

Math

Hints open one at a time

Hint 1

Reverse each digit with their corresponding new digit if an invalid digit is found the return -1. After reversing the digits just compare the reversed number with the original number.

15:41

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