Is Strobogrammatic Number easy or hard?

Strobogrammatic Number is classified as an Easy problem on LeetCode with an acceptance rate around 47%. The challenge is recognizing valid digit rotations and applying a two-pointer symmetry check efficiently.

Strobogrammatic Number Python/Java solution

In Python or Java, define a mapping of valid rotated digits and use two pointers moving inward. For each pair, verify that map[leftDigit] equals rightDigit. If any pair fails or a digit is not in the mapping, return false; otherwise return true after scanning the string.

How to solve Strobogrammatic Number in O(n)?

Use two pointers scanning from both ends of the string. Maintain a mapping of valid rotations: 0→0, 1→1, 6→9, 8→8, and 9→6. For each step, confirm that the left digit rotates to the right digit. Continue until the pointers cross; if all pairs match, the number is strobogrammatic.

What is the best approach for Strobogrammatic Number?

The two pointers simulation is the best approach. Start one pointer at the beginning and another at the end, then check whether each pair of digits forms a valid rotated pair such as (6,9) or (1,1). This method runs in O(n) time and uses O(1) space because it avoids building a new string.

Is Strobogrammatic Number asked at Google/Amazon/Meta?

Strobogrammatic Number appears in coding interview preparation lists and is commonly associated with companies like Google and Amazon in online interview archives. Variants such as generating all strobogrammatic numbers are also asked to test string manipulation and symmetry logic.

What data structure is used in Strobogrammatic Number?

A hash table (or dictionary) is typically used to store valid digit rotations such as 6→9 and 9→6. The algorithm then uses two pointers on the string to validate mirrored digits using constant-time hash lookups.

What is the time complexity of Strobogrammatic Number?

The optimal solution runs in O(n) time where n is the number of digits in the string. Each pair of digits is checked once using a constant-time lookup from a digit rotation map. Space complexity can be O(1) with the two-pointer method.

Description Solution Video 9:50

246. Strobogrammatic Number

Easy47.6% acceptance2 companiesPremium elsewhere, free here

Given a string num which represents an integer, return true if num is a strobogrammatic number.

A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down).

Example 1:

Input: num = "69"
Output: true

Example 2:

Input: num = "88"
Output: true

Example 3:

Input: num = "962"
Output: false

Constraints:

1 <= num.length <= 50
num consists of only digits.
num does not contain any leading zeros except for zero itself.

Asked at 2 companies

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9:50

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246. Strobogrammatic Number

Asked at 2 companies

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