Leetcode 246: Strobogrammatic Number

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.

 

public class Solution {
    public bool IsStrobogrammatic(string num) {
        if (num == null || num.Length == 0) return true;
        
        int i = 0, j = num.Length - 1;
        
        while (i <= j)
        {
            if ((num[i] == '6' && num[j] == '9') || (num[i] == '9' && num[j] == '6') || (num[i] == '8' && num[j] == '8') || (num[i] == '0' && num[j] == '0') || (num[i] == '1' && num[j] == '1'))
            {
                i++;
                j--;
            }
            else
            {
                return false;
            }
        }
        
        return true;
    }
}