[LintCode] Problem 644 - Strobogrammatic Number

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A mirror number is a number that looks the same when rotated 180 degrees (looked at upside down).For example, the numbers “69”, “88”, and “818” are all mirror numbers.

Write a function to determine if a number is mirror. The number is represented as a string.

Example

No.1

Input : “69”

Output : true

No.2

Input : “68”

Output : false

Code

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

    int i = 0;
    int j = num.length() - 1;

    while (i <= j) {
        if (!map.containsKey(num.charAt(i)) || map.get(num.charAt(i)) != num.charAt(j))
            return false;

        i++;
        j--;
    }

    return true;
}