StrobogrammaticNumber.java

package com.fishercoder.solutions;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

/**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.

 For example, the numbers "69", "88", and "818" are all strobogrammatic.*/

public class StrobogrammaticNumber {

    public boolean isStrobogrammatic_map(String num) {
        int i = 0, j = num.length()-1;
        Map<Character, Character> map = new HashMap();
        map.put('8', '8');
        map.put('1', '1');
        map.put('0', '0');
        if(j == 0) return map.containsKey(num.charAt(i));
        
        map.put('9', '6');
        map.put('6', '9');
        while(i < j){
            if(!map.containsKey(num.charAt(i)) || !map.containsKey(num.charAt(j))) return false;
            if(map.get(num.charAt(i)) != num.charAt(j)) return false;
            i++;j--;
        }
        return map.containsKey(num.charAt(i));
    }

    
    public boolean isStrobogrammatic_set(String num) {
        Set<Character> set = new HashSet();
        set.add('0');
        set.add('1');
        set.add('6');
        set.add('8');
        set.add('9');
        char[] nums = num.toCharArray();
        int i = 0, j = num.length()-1;
        while(i <= j){
            if(!set.contains(nums[i]) || !set.contains(nums[j])) return false;
            if(nums[i] == '6' && nums[j] != '9') return false;
            else if(nums[i] == '9' && nums[j] != '6') return false;
            else if(nums[i] == '1' && nums[j] != '1') return false;
            else if(nums[i] == '8' && nums[j] != '8') return false;
            else if(nums[i] == '0' && nums[j] != '0') return false;
            else {
                i++; j--;
            }
        }
        return true;
    }
}