246. Strobogrammatic Number_HashMap＜＞()

Given a string num which represents an integer, return true if num is a strobogrammatic number.

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

Example One:

Input: num = "69"
Output: true



Example Two:

Input: num = "88"
Output: true


Example Three:

Input: num = "962"
Output: false

Solutions:

class Solution {
    public boolean isStrobogrammatic(String num) {
       
        Map<Character, Character> map = Map.of('1','1','0','0','6','9','9','6','8','8');
        StringBuilder  str = new StringBuilder();

        int len = num.length();
        char c = 0;
        for(int i = len -1; i >= 0; i--){
            c = num.charAt(i);
            if(!map.containsKey(c)) return false;
            else str.append(map.get(c));
        }
        String result = str.toString();
        return result.equals(num);
        

    }
}

Hints:

Logics:

• Hava a HashMap to restore the character that a strobogrammatic number
• The characters of '9' and '6' are the special ones
• Have a String Builder that will store the characters that are rotated 180 degrees
• compare the result with num

Tips:

• Set up the HashMap: Map<Character, Character> map = Map.of('1','1','0','0','6','9','9','6','8','8'); instead of using map.put() method
• use str.toString() to convert the char to string
• use .equals() method to compare the result
• return the boolean result