CareerCup

For 1st part:
If one digit represents 3 letters. So, 4 digit will represent 3^4 combinations of strings. We can do that in a for loop ?

For 2nd part:
After getting output from 1st part, we can check if (combination present in dict. ) ?
and output accordingly. ?

public class Phone2Text {
	private static String[] mapping = { "ABC", "DEF", "GHI", "JKL", "MNO",
			"PQR", "STU", "VW", "XY", "Z*#" };

	public static void combinations(int[] number, char[] buf, int numIndex) {

		for (int i = 0; i < mapping[number[numIndex]].length(); i++) {
			buf[numIndex] = mapping[number[numIndex]].charAt(i);
			if (numIndex < number.length - 1) {
				combinations(number, buf, numIndex + 1);
			} else
				System.out.println(buf);
		}
	}

	public static void main(String[] args) {
		int num[] = { 5, 8, 5, 5, 0, 3, 3, 4, 4, 7 };
		Phone2Text.combinations(num, new char[num.length], 0);
	}
}

#pay attention to the mapping.

Build a trie by number instead of character

python:

n2l = { 1:"ABC", 2:"DF", 3:"GHI", 4:"JKL", 5:"MNO", 6:"PQR", 7:"STU"}
   
def gen(S,G=''):
    if not S:
        print G
        return
    else:
        for l in n2l[int(S[0])]:
            gen(S[1:], G+l)
gen("123")

<pre lang="" line="1" title="CodeMonkey23618" class="run-this">import Data.Array (listArray, (!))
import Data.Char (digitToInt)
import Data.Set (fromList, member)

keyMap = listArray (2, 9) ["ABC", "DEF", "GHI", "JKL", "MNO", "PQRS", "TUV", "WXYZ"]

digitCombinations digits = sequence $ [keyMap ! i | i <- digits]

dictionary = fromList ["DOG", "CAT", "BIRD", "REPTILE"]

main = do
numberString <- getLine
let numberCombinations = digitCombinations $ map digitToInt numberString
return $ filter ((flip member) dictionary) numberCombinations
</pre><pre title="CodeMonkey23618" input="yes">
</pre>

string lookup[10] = {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};

int coi(char c){
	return ((int)c - 48);
}

void print(string oldString, string newString)
{
	if (oldString.length() == 0) {
		cout << newString << endl;
		return;
	}
	else {
		string characters = lookup[coi(oldString[0])];
		int numOfChars = characters.length();
		
		for(int i=0; i<numOfChars; ++i)
		{
			print(oldString.substr(1),newString+characters[i]);
		}
	}
}