[LC] 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.

Example 1:

Input:  "69"
Output: true

Example 2:

Input:  "88"
Output: true

Example 3:

Input:  "962"
Output: false

class Solution {
    public boolean isStrobogrammatic(String num) {
        Map<Character, Character> mymap = new HashMap<>();
        mymap.put('1', '1');
        mymap.put('8', '8');
        mymap.put('0', '0');
        mymap.put('6', '9');
        mymap.put('9', '6');
        int left = 0;
        int right = num.length() - 1;
        while (left <= right) {
            char left_char = num.charAt(left);
            char right_char = num.charAt(right);
            if (!mymap.containsKey(left_char) || !mymap.containsKey(right_char)) {
                return false;
            } else if (mymap.get(left_char) != right_char) {
                return false;
            }
            left += 1;
            right -= 1;
        }
        return true;
    }
}