Problem Description:

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

Write a function to determine if a number is strobogrammatic. The number is represented as a string.

For example, the numbers "69", "88", and "818" are all strobogrammatic.

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The following is the C++ implementation of the suggested solution using a look-up table (implemented as an unordered_map). It takes 0 ms. But, I wonder, are there any real applications of strobogrammatic numbers?

1 class Solution { 2 public: 3     bool isStrobogrammatic(string num) { 4         make_lut(); 5         int n = num.length();  6         for (int l = 0, r = n - 1; l <= r; l++, r--) 7             if (lut.find(num[l]) == lut.end() || lut[num[l]] != num[r]) 8                 return false; 9         return true;10     }11 private:12     unordered_map
     
       lut; 13     void make_lut(void) {14         lut['0'] = '0';15         lut['1'] = '1';16         lut['6'] = '9';17         lut['8'] = '8';18         lut['9'] = '6';19     }20 };