Strobogramattic.java

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

INTUITON, make a map of all th valid keys and their opposite value
then use, TWO POINTERS to check from start and end if they are equal 
 
//TC: O(N) to go through the length of the string
//SC: O(1) because constant map space 

class Solution {
 public boolean isStrobogrammatic(String num) {
    Map<Character, Character> map = new HashMap<Character, Character>();
    map.put('6', '9');
    map.put('9', '6');
    map.put('0', '0');
    map.put('1', '1');
    map.put('8', '8');
   
    int l = 0, r = num.length() - 1;
    while (l <= r) {
        if (!map.containsKey(num.charAt(l))) return false;
        if (map.get(num.charAt(l)) != num.charAt(r))
            return false;
        l++;
        r--;
    }
    
    return true;
}
}