refactor 1392

fishercoder1534 · fishercoder1534 · commit 846852454399 · 2020-03-22T11:03:10.000-07:00
diff --git a/README.md b/README.md
@@ -8,7 +8,7 @@ _If you like this project, please leave me a star._ &#9733;
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|--------|-------------|-------------
-|1392|[Longest Happy Prefix](https://leetcode.com/problems/longest-happy-prefix/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1392.java) | |Hard|String|
+|1392|[Longest Happy Prefix](https://leetcode.com/problems/longest-happy-prefix/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1392.java) | |Hard|String, Rolling Hash|
 |1390|[Four Divisors](https://leetcode.com/problems/four-divisors/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1390.java) | |Medium|Math|
 |1389|[Create Target Array in the Given Order](https://leetcode.com/problems/create-target-array-in-the-given-order/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1389.java) | |Easy|Array|
 |1388|[Pizza With 3n Slices](https://leetcode.com/problems/pizza-with-3n-slices/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1388.java) | |Hard|DP|
diff --git a/src/main/java/com/fishercoder/solutions/_1392.java b/src/main/java/com/fishercoder/solutions/_1392.java
@@ -33,18 +33,19 @@ public class _1392 {
     public static class Solution1 {
         /**credit: https://leetcode.com/problems/longest-happy-prefix/discuss/547446/C%2B%2BJava-Incremental-Hash-and-DP*/
         public String longestPrefix(String s) {
-            long headHash = 0;
-            long tailHash = 0;
+            int times = 2;
+            long prefixHash = 0;
+            long suffixHash = 0;
             long multiplier = 1;
             long len = 0;
             long mod = 1000000007;//use some large prime as a modulo to avoid overflow errors, e.g. 10 ^ 9 + 7.
             for (int i = 0; i < s.length() - 1; i++) {
-                headHash = (headHash * 26 + s.charAt(i)) % mod;
-                tailHash = (multiplier * s.charAt(s.length() - i - 1) + tailHash) % mod;
-                if (headHash == tailHash) {
+                prefixHash = (prefixHash * times + s.charAt(i)) % mod;
+                suffixHash = (multiplier * s.charAt(s.length() - i - 1) + suffixHash) % mod;
+                if (prefixHash == suffixHash) {
                     len = i + 1;
                 }
-                multiplier = multiplier * 26 % mod;
+                multiplier = multiplier * times % mod;
             }
             return s.substring(0, (int) len);
         }
diff --git a/src/test/java/com/fishercoder/_1392Test.java b/src/test/java/com/fishercoder/_1392Test.java
