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letterCombinations.java

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package Algorithms;

import java.util.ArrayList;

public class letterCombinations {

public static void main(String[] args){

JavaAppWithoutMain test = new JavaAppWithoutMain();

String digits = "234";

ArrayList<String> result = letterCombinations(digits);

for(int i = 0; i < result.size(); i ++){

System.out.printf("%d: %s\n",i, result.get(i));

}

public static ArrayList<String> letterCombinations(String digits) {

String[] charas = new String[]{"abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};

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

StringBuilder exitStr = new StringBuilder();

int pos = 0;

String[] inputStr = new String[digits.length()];

for (int i = 0; i < digits.length(); i ++){

int index = (int)digits.charAt(i) - 46 - 4;

System.out.printf("index %d\n",index);

inputStr[i] = charas[index];

}

letterCombinationHelp(result, exitStr, inputStr, pos);

return result;

}

public static void letterCombinationHelp(ArrayList<String> result,

StringBuilder exitStr,String[] inputStr, int pos){

StringBuilder strBuilder = new StringBuilder();

if (inputStr.length == 0){

return;

}

if (exitStr.length() == inputStr.length){

result.add(new String(exitStr));

return;

}

for (int j = 0; j < inputStr[pos].length(); j++){

exitStr.append(inputStr[pos].charAt(j));

letterCombinationHelp(result, exitStr, inputStr, pos + 1);

// remove the appended char

exitStr.deleteCharAt(exitStr.length() - 1);

}