CareerCup

function get180(num){
    if(num === 0) return [];
    if(num === 1) return ["0", "1", "8"];
    if(num === 2) return ["00", "11", "69", "96", "88"];

    return jamHelper(get180(num - 2));
}

function jamHelper(array){
    var obj = {
        "0": "0",
        "1": "1",
        "8": "8",
        "9": "6",
        "6": "9"
    }
    var holder = [];
    for(var i = 0; i < array.length; i++){
        for(key in obj){
            holder.push(`${key}${array[i]}${obj[key]}`)
        }
    }
    return holder;
}

printOneEighty :: Int -> [String]
printOneEighty 0 = [""]
printOneEighty 1 = ["0","1","8"]
printOneEighty k = let temp = printOneEighty $ k - 2
                   in foldl appendDigits [] temp
                   where 
                   appendDigits acc str = acc  ++ added str
                   added str = [(show . fst $ pair) ++ str ++ (show . snd $ pair) | pair <- [(0,0),(1,1),(8,8),(6,9),(9,6)]]

main = do
  putStrLn . show . printOneEighty $ 5

//prints ["00000","10001","80008","60009","90006","01010","11011","81018","61019","91016","08080","18081","88088","68089","98086","06090","16091","86098","66099","96096","09060","19061","89068","69069","99066","00100","10101","80108","60109","90106","01110","11111","81118","61119","91116","08180","18181","88188","68189","98186","06190","16191","86198","66199","96196","09160","19161","89168","69169","99166","00800","10801","80808","60809","90806","01810","11811","81818","61819","91816","08880","18881","88888","68889","98886","06890","16891","86898","66899","96896","09860","19861","89868","69869","99866"]

NUM_LIST = ["0", "1", "6", "8", "9"]
UPSIDE_DOWN = {
    "0" : "0",
    "1" : "1",
    "6" : "9",
    "8" : "8",
    "9" : "6"
}

def get180(digits):
    """
    Return numbers with specified digits that look the same upside down
    """
    if digits == 0:
        return ['']

    if digits == 1:
        return filter(lambda x: UPSIDE_DOWN[x] == x, NUM_LIST)

    middle_list = get180(digits - 2)
    result_list = []
    for number in NUM_LIST:
        for middle in middle_list:
            result_list.append(number + middle + UPSIDE_DOWN[number])
    return result_list

public class UpsideDownString {
    private Map<String, String> reverseMap;

    public UpsideDownString() {
        reverseMap = new HashMap<>();
        reverseMap.put("8", "8");
        reverseMap.put("6", "9");
        reverseMap.put("0", "0");
        reverseMap.put("1", "1");
    }

    public ArrayList<String> solve(int n) {
        if (n == 0) return new ArrayList<>();
        if (n == 1) return new ArrayList<String>(Arrays.asList("8", "0", "1"));
        if (n == 2) return new ArrayList<>(Arrays.asList("00", "11", "69", "96", "88"));

        // we will solve sub problem with n-2 characters. 
        // after that we append 2 char onto left-most and right-most
        ArrayList<String> upsideDownStrings = solve(n - 2);

        ArrayList<String> res = new ArrayList<String>();
        for (String str : upsideDownStrings) {
            for (Map.Entry entry : reverseMap.entrySet()) {
                String key = (String) entry.getKey();
                String value = (String) entry.getValue();
                String newReversible = key + str + value;
                res.add(newReversible);
            }
        }
        
        return res;
    }
}

public class Solution{
	static Map<String, String> map = new HashMap<String,String>();
	static {
		map.put("0", "0");
		map.put("1", "1");
		map.put("6", "9");
		map.put("9", "6");
		map.put("8", "8");
	}
	
	public static List<String> generate(int k){
		if(k == 0) return new ArrayList<String>();
		if(k == 1) return new ArrayList<String>(Arrays.asList("0","1","8"));
	
		List<String> result = new ArrayList<String>();
		List<String> subList = generate(k-2);
		for(Entry<String, String> entry : map.entrySet()){
			if(subList.isEmpty()){
				String tmp = entry.getKey() + entry.getValue(); 
				result.add(tmp);
			}
			for(String s : subList){
				String tmp = entry.getKey() + s + entry.getValue(); 
				result.add(tmp);
			}
		}
		return result;
	}
	
	public static void main(String[] args){
		System.out.println(generate(2));
	}

}

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