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/*

Runtime: 32 ms, faster than 8.05% of Java online submissions for Letter Combinations of a Phone Number.

Memory Usage: 35.3 MB, less than 89.31% of Java online submissions for Letter Combinations of a Phone Number.

Next challenges:

*/

import java.util.*;

class LeetCode17{

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

List<String> result = new LinkedList<String>();

HashMap<Character, List<Character>> map = new HashMap<>();

map.put('2',Arrays.asList('a','b','c'));

map.put('3',Arrays.asList('d','e','f'));

map.put('4',Arrays.asList('g','h','i'));

map.put('5',Arrays.asList('j','k','l'));

map.put('6',Arrays.asList('m','n','o'));

map.put('7',Arrays.asList('p','q','r','s'));

map.put('8',Arrays.asList('t','u','v'));

map.put('9',Arrays.asList('w','x','y','z'));

if(digits.isEmpty()) return result;

solve(digits, "",map , 0, result);

return result;

}

public static void solve(String digits,String currentstring, HashMap<Character,List<Character>> map, int position,List<String> result){

char ch = digits.charAt(position);

List<Character> chlist = map.get(ch);

if(position==digits.length()-1) {

chlist.forEach((letter)->{

result.add(currentstring+letter);

});

}else{

chlist.forEach((letter)->{

solve(digits,currentstring+letter,map,position+1,result);

});

}

}

public static void main(String[] args){

List<String> list = new LinkedList<String>();

String d1 = "23";

String d2 = "22333";

list = letterCombinations(d1);

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

System.out.println(list.get(i));

}

list = letterCombinations(d2);

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

System.out.println(list.get(i));

}

}

}