LeetCode [246] Strobogrammatic Number

246. Strobogrammatic Number

Easy

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: num = "69"
Output: true

Example 2:

Input: num = "88"
Output: true

Example 3:

Input: num = "962"
Output: false

Example 4:

Input: num = "1"
Output: true

//Java
class Solution {
    Map<Character, Character> map = new HashMap<>();
    public boolean isStrobogrammatic(String num) {
        map.put('0', '0');
        map.put('1', '1');
        map.put('6', '9');
        map.put('8', '8');
        map.put('9', '6');

        StringBuilder ret = new StringBuilder();
        for(int i=num.length()-1; i>=0; --i){
            char c = num.charAt(i);
            if(!map.containsKey(c)) return false;
            ret.append(map.get(c));
        }

        return ret.toString().equals(num.toString());
    }
}

//C++
//C++: 0ms
class Solution {
public:
    bool isStrobogrammatic(string num) {
        int n = num.size(), l = 0, r = n-1;
        while(l<=r){
            if(num[l]==num[r] && num[l]!='0' && num[l]!='1' && num[l]!='8') return false;
            if(num[l]!=num[r] && !((num[l]=='6'&&num[r]=='9')||(num[l]=='9'&&num[r]=='6'))) return false;
            l++;
            r--;
        }
        return true;
    }
};