leetcode

commit b284a4bfdb97fdf2da5d6746ee5f231a0eb66ea6
parent 8b5d3f89b4869d3cb0ed361cfc8f45f68fb05511
Author: AndrewLockVI <andrewlaack1@gmail.com>
Date:   Sat,  6 May 2023 22:04:40 -0500

Completed longest palindromic substring using dart

Diffstat:
A
longest-palindromic-substring/longest-palindromic-substring.dart
 | 
54
++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 54 insertions(+), 0 deletions(-)
diff --git a/longest-palindromic-substring/longest-palindromic-substring.dart b/longest-palindromic-substring/longest-palindromic-substring.dart
@@ -0,0 +1,54 @@
+//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;
+    }
+}