implemented findPermutationDifference method in Lesson13.java file

Author: mercedes-mathews

lesson_13/maps_java/maps_app/src/main/java/com/codedifferently/lesson13/Lesson13.java

@@ -1,12 +1,27 @@
 package com.codedifferently.lesson13;
 
+import java.util.HashMap;
+
 public class Lesson13 {
 
   /**
    * Provide the solution to LeetCode 3146 here:
    * https://leetcode.com/problems/permutation-difference-between-two-strings
    */
   public int findPermutationDifference(String s, String t) {
-    return 0;
+    var sIndexByLetter = new HashMap<Character, Integer>();
+    var tIndexByLetter = new HashMap<Character, Integer>();
+
+    for (int i = 0; i < s.length(); i++) {
+      sIndexByLetter.put(s.charAt(i), i);
+      tIndexByLetter.put(t.charAt(i), i);
+    }
+
+    int sum = 0;
+    for (char c : s.toCharArray()) {
+      sum += Math.abs(sIndexByLetter.get(c) - tIndexByLetter.get(c));
+    }
+
+    return sum;
   }
 }