Practice/Meta/Leetcode 246. Strobogrammatic Number

Leetcode 246. Strobogrammatic Number

CodingMust

Problem

A mirror number is a number that looks identical when rotated 180 degrees. When certain digits are rotated, they transform according to these rules:

• 0 rotates to 0
• 1 rotates to 1
• 6 rotates to 9
• 8 rotates to 8
• 9 rotates to 6

All other digits (2, 3, 4, 5, 7) become invalid when rotated 180 degrees.

Given a string representing a numeric value, determine whether it qualifies as a mirror number. The number should appear identical when the entire string is rotated 180 degrees.

Requirements

1. Return true if the number is a valid mirror number, false otherwise
2. Handle single-digit numbers appropriately
3. Check that all digits in the number can be validly rotated
4. Ensure the rotated result matches the original when read in reverse

Constraints

• 1 ≤ num.length ≤ 50
• num consists of only digits
• num does not contain leading zeros except when the number itself is "0"
• Expected time complexity: O(n) where n is the length of the string
• Expected space complexity: O(1)

Examples

Example 1:

Input: num = "69" Output: true Explanation: When rotated 180 degrees, 6 becomes 9 and 9 becomes 6. Reading the rotated result from right to left gives "69", which matches the original.

Example 2:

Input: num = "88" Output: true Explanation: Each 8 remains an 8 when rotated. The number reads the same after rotation.

Example 3:

Input: num = "962" Output: false Explanation: The digit 2 cannot be rotated to form a valid digit, so this is not a mirror number.

Example 4:

Input: num = "1" Output: true Explanation: The digit 1 looks the same when rotated 180 degrees.