[LintCode] Mirror Numbers

A mirror 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 mirror. The number is represented as a string.

 

Example

For example, the numbers "69", "88", and "818" are all mirror numbers.
Given num = "69" return true
Given num = "68" return false

 

The allowed mapping is:

6 -> 9 

9 -> 6

0 -> 0

1 -> 1

8 -> 8

 

Use a hash map to store the above mapping and go through the input string. If a character has no mappings or 

its mapped character is not the same with the character at its symmetric right side , return false.

 

public 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 left = 0, right = num.length() - 1;
        while (left <= right) {
            if (!map.containsKey(num.charAt(left))) {
                return false;
            }
            if (map.get(num.charAt(left)) != num.charAt(right)) {
                return false;
            }
            left++;
            right--;
        }
        return true;
    }
}

 

Related Problems

[LeetCode]Strobogrammatic Number II

[LeetCode]Strobogrammatic Number III