leetcode

longest-palindromic-substring.dart (1886B)

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 //Longest palindromic substring solution using dart.
 //Find the longest palindrome contained in a string and return it.
 //The solution I used to this problem was to place all indexes of characters into a map.
 //I then iterated through the string again and each repeat value is checked to see if it creates a palindrome.
 class Solution {
   String longestPalindrome(String s) {
       String longest = "";
       Map <String, List<int>> characters = {};
       for(int i = 0 ; i < s.length ; ++i){
           if(characters[s[i]] != null){
               characters[s[i]]?.add(i);
           }
           else{
               characters[s[i]] = [i];
           }
       }
       for(int i = 0 ; i < s.length ; ++i){
           if((characters[s[i]]?.length ?? 0) >= 2){
               List<int> indexes = characters[s[i]] ?? [];
               for(int x = 0 ; x < indexes.length ; ++x){
                   for(int z = indexes.length - 1; z > x ; --z){
                       if((indexes[z] - indexes[x]).abs()  >= longest.length){
                         String sub = s.substring(indexes[x] , indexes[z] + 1);
                             if(isPalindrome(sub)){
                                 longest = sub;
                             }
                         }
                       }
                   }
               }
           }
           if(longest == "" && s.length > 0){
               return s[0];
           }
           return longest;
       }
     bool isPalindrome(String check){
         if(check.length == 1){
             return true;
         }
         if(check.length == 2){
             if(check[0] == check[1]){
                 return true;
             }
             return false;
         }
         for(int i = 0 ; i < check.length / 2 + 1 ; ++i){
             if(check[i] != check[check.length - 1 - i]){
                 return false;
             }    
         }
         return true;
     }
 }