Add solution #1392

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,275 LeetCode solutions in JavaScript
+# 1,276 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1062,6 +1062,7 @@
 1389|[Create Target Array in the Given Order](./solutions/1389-create-target-array-in-the-given-order.js)|Easy|
 1390|[Four Divisors](./solutions/1390-four-divisors.js)|Medium|
 1391|[Check if There is a Valid Path in a Grid](./solutions/1391-check-if-there-is-a-valid-path-in-a-grid.js)|Medium|
+1392|[Longest Happy Prefix](./solutions/1392-longest-happy-prefix.js)|Hard|
 1400|[Construct K Palindrome Strings](./solutions/1400-construct-k-palindrome-strings.js)|Medium|
 1402|[Reducing Dishes](./solutions/1402-reducing-dishes.js)|Hard|
 1408|[String Matching in an Array](./solutions/1408-string-matching-in-an-array.js)|Easy|

solutions/1392-longest-happy-prefix.js

@@ -0,0 +1,32 @@
+/**
+ * 1392. Longest Happy Prefix
+ * https://leetcode.com/problems/longest-happy-prefix/
+ * Difficulty: Hard
+ *
+ * A string is called a happy prefix if is a non-empty prefix which is also a suffix
+ * (excluding itself).
+ *
+ * Given a string s, return the longest happy prefix of s. Return an empty string ""
+ * if no such prefix exists.
+ */
+
+/**
+ * @param {string} s
+ * @return {string}
+ */
+var longestPrefix = function(s) {
+  let prefixLength = 0;
+  const prefixHash = new Array(s.length).fill(0);
+
+  for (let i = 1; i < s.length; i++) {
+    while (prefixLength > 0 && s[i] !== s[prefixLength]) {
+      prefixLength = prefixHash[prefixLength - 1];
+    }
+    if (s[i] === s[prefixLength]) {
+      prefixLength++;
+    }
+    prefixHash[i] = prefixLength;
+  }
+
+  return s.slice(0, prefixHash[s.length - 1]);
+};