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import java.util.ArrayList;

/*

* Letter Combinations of a Phone Number

* Given a digit string

* return all possible letter combinations that the number could represent

* Input:Digit string "23"

* Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]

*/

public class Solution25 {

public ArrayList<String> letterCombinations(String digits) {

ArrayList<String> result = new ArrayList<String>();

if (!digits.equals("")) {

int length = digits.length();

char[][] c = {{' '},{' '},{'a','b','c'},{'d','e','f'},{'g','h','i'},

{'j','k','l'},{'m','n','o'},{'p','q','r','s'},{'t','u','v'},

{'w','x','y','z'}};

int[] total = {0,0,3,3,3,3,3,4,3,4};

int[] number = new int[length];

int[] answer = new int[length];

for (int i = 0; i < length; i++)

number[i] = digits.charAt(i) - '0';

while (true) {

String temp = "";

for (int i = 0; i < length; i++)

temp += c[number[i]][answer[i]];

result.add(temp);

int k = length - 1;

while (k >= 0) {

if (answer[k] < total[number[k]] - 1) {

answer[k]++;

break;

} else {

answer[k] = 0;

k--;

}

}

if (k < 0)

break;

}

} else

result.add("");

return result;

}

public static void main(String ...args) {

Solution25 s25 = new Solution25();

s25.letterCombinations("23");

}

}