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Grokking the Coding Interview Patterns in C#

Solution: Strobogrammatic Number

Explore how to use the two pointer technique to identify if a string representing a number is strobogrammatic. Understand the process of matching digits from both ends toward the center, using predefined digit mappings that allow rotation by 180 degrees. This lesson helps you develop an efficient approach to solve such problems with a time complexity of O(n) and constant space usage.

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Statement

Given a string num representing an integer, determine whether it is a strobogrammatic number. Return TRUE if the number is strobogrammatic or FALSE if it is not.

Note: A strobogrammatic number appears the same when rotated 180180 degrees (viewed upside down). For example, “69” is strobogrammatic because it looks the same when flipped upside down, while “962” is not.

Constraints:

  • 1<=1 <= num.length <=50<= 50

  • num contains only digits.

  • num has no leading zeros except when the number itself is zero.

Solution

The solution uses a two pointer approach to determine whether a given string num is a strobogrammatic number by checking its digits from both ends toward the center. It uses a set of valid digit mappings that remain unchanged when rotated 180180 degrees or transform into each other when flipped (such as ′0′'0' ...