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Grokking the Coding Interview Patterns in C++

Solution: Strobogrammatic Number

Explore how to use the two pointers technique to check if a number is strobogrammatic. Learn to compare digit pairs from the ends toward the center, verifying rotated mappings. This lesson helps you implement an efficient solution with O(n) time and O(1) space complexity.

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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' ...