feat: Adds Nana's Lesson13.java homework

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

@@ -1,12 +1,29 @@
 package com.codedifferently.lesson13;
 
+import java.util.HashMap;
+import java.util.Map;
+
 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;
+    Map<Character, Integer> smap = new HashMap<>();
+    for (int i = 0; i < s.length(); i++) {
+      char c = s.charAt(i);
+      smap.put(c, i);
+    }
+    Map<Character, Integer> tmap = new HashMap<>();
+    for (int i = 0; i < t.length(); i++) {
+      char c = t.charAt(i);
+      tmap.put(c, i);
+    }
+    int ans = 0;
+    for (char c : smap.keySet()) {
+      ans = ans + Math.abs(smap.get(c) - tmap.get(c));
+    }
+    return ans;
   }
 }