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letter-combinations-of-a-phone-number.dart (1368B)

      1 //Given a list of numbers return all possible permutations that could result from the given inputs assuming that
      2 //each number can be any of the associated letters when looking at an old phone where you can access letters by
      3 //repeating numbers.
      4 //Time: 247ms Beats: 77.78%
      5 //Memory: 141MB Beats: 38.89%
      6 
      7 class Solution {
      8   Map<int , List<String>> options = {};
      9   int original_length = -1;
     10   Solution(){
     11       options = {
     12           2 : ["a" , "b" , "c"],
     13           3 : ["d" , "e" , "f"],
     14           4 : ["g" , "h" , "i"],
     15           5 : ["j" , "k" , "l"],
     16           6 : ["m" , "n" , "o"],
     17           7 : ["p" , "q" , "r" , "s"],
     18           8 : ["t" , "u" , "v"],
     19           9 : ["w" , "x" , "y" , "z"]
     20       };
     21   }
     22   List<String> letterCombinations(String digits) {
     23     if(original_length == -1){
     24         original_length = digits.length;
     25         if(digits.length == 0){
     26             return [];
     27         }
     28     }
     29     if(digits.length == 0){
     30         return [""];
     31     }
     32     List<String> ret_list = [];
     33     String new_digits = digits.substring(1);
     34     List<String> vals = (options[int.parse(digits[0])] ?? []);
     35     for(int x = 0 ; x < vals.length ; ++x){
     36         List<String> returned_list = letterCombinations(new_digits);
     37         for(int y = 0 ; y < returned_list.length ; ++y){
     38             ret_list.add(vals[x] + returned_list[y]);
     39         }
     40     }
     41       return ret_list;
     42   }
     43 }