solves #3146: Permutation Difference between Two Strings in java

Author: anishLearnsToCode

Diff for: README.md

@@ -910,7 +910,7 @@
 | 3131 | [Find the Integer Added to Array I](https://leetcode.com/problems/find-the-integer-added-to-array-i)                                                                   |                                                                                 [![Java](assets/java.png)](src/FindTheIntegerAddedToArrayI.java)                                                                                 |                                                                                                                                   |
 | 3136 | [Valid Word](https://leetcode.com/problems/valid-word)                                                                                                                 |                                                                                          [![Java](assets/java.png)](src/ValidWord.java)                                                                                          |                                                                                                                                   |
 | 3142 | [Check if Grid Satisfies Conditions](https://leetcode.com/problems/check-if-grid-satisfies-conditions)                                                                 |                                                                               [![Java](assets/java.png)](src/CheckIfGridSatisfiesConditions.java)                                                                                |                                                                                                                                   |
-| 3146 | [Permutation Difference between Two Strings](https://leetcode.com/problems/permutation-difference-between-two-strings)                                                 |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 3146 | [Permutation Difference between Two Strings](https://leetcode.com/problems/permutation-difference-between-two-strings)                                                 |                                                                           [![Java](assets/java.png)](src/PermutationDifferenceBetweenTwoStrings.java)                                                                            |                                                                                                                                   |
 | 3151 | [Special Array I](https://leetcode.com/problems/special-array-i)                                                                                                       |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 3158 | [Find the XOR of Numbers Which Appear Twice](https://leetcode.com/problems/find-the-xor-of-numbers-which-appear-twice)                                                 |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 3162 | [Find the Number of Good Pairs I](https://leetcode.com/problems/find-the-number-of-good-pairs-i)                                                                       |                                                                                                                                                                                                                                  |                                                                                                                                   |

Diff for: src/PermutationDifferenceBetweenTwoStrings.java

@@ -0,0 +1,27 @@
+// https://leetcode.com/problems/permutation-difference-between-two-strings
+// T: O(N)
+// S: O(1)
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class PermutationDifferenceBetweenTwoStrings {
+    public int findPermutationDifference(String s, String t) {
+        final Map<Character, Integer> letterIndexes = getCharacterIndexMapping(s);
+        int sum = 0;
+
+        for (int i = 0 ; i < t.length() ; i++) {
+            sum += Math.abs(i - letterIndexes.get(t.charAt(i)));
+        }
+
+        return sum;
+    }
+
+    private static Map<Character, Integer> getCharacterIndexMapping(String s) {
+        final Map<Character, Integer> map = new HashMap<>();
+        for (int i = 0 ; i < s.length() ; i++) {
+            map.put(s.charAt(i), i);
+        }
+        return map;
+    }
+}