Add solution #2014

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,688 LeetCode solutions in JavaScript
+# 1,689 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1545,6 +1545,7 @@
 2011|[Final Value of Variable After Performing Operations](./solutions/2011-final-value-of-variable-after-performing-operations.js)|Easy|
 2012|[Sum of Beauty in the Array](./solutions/2012-sum-of-beauty-in-the-array.js)|Medium|
 2013|[Detect Squares](./solutions/2013-detect-squares.js)|Medium|
+2014|[Longest Subsequence Repeated k Times](./solutions/2014-longest-subsequence-repeated-k-times.js)|Hard|
 2016|[Maximum Difference Between Increasing Elements](./solutions/2016-maximum-difference-between-increasing-elements.js)|Easy|
 2017|[Grid Game](./solutions/2017-grid-game.js)|Medium|
 2027|[Minimum Moves to Convert String](./solutions/2027-minimum-moves-to-convert-string.js)|Easy|

solutions/2014-longest-subsequence-repeated-k-times.js

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+/**
+ * 2014. Longest Subsequence Repeated k Times
+ * https://leetcode.com/problems/longest-subsequence-repeated-k-times/
+ * Difficulty: Hard
+ *
+ * You are given a string s of length n, and an integer k. You are tasked to find the longest
+ * subsequence repeated k times in string s.
+ *
+ * A subsequence is a string that can be derived from another string by deleting some or no
+ * characters without changing the order of the remaining characters.
+ *
+ * A subsequence seq is repeated k times in the string s if seq * k is a subsequence of s,
+ * where seq * k represents a string constructed by concatenating seq k times.
+ * - For example, "bba" is repeated 2 times in the string "bababcba", because the string
+ *   "bbabba", constructed by concatenating "bba" 2 times, is a subsequence of the
+ *   string "bababcba".
+ *
+ * Return the longest subsequence repeated k times in string s. If multiple such subsequences
+ * are found, return the lexicographically largest one. If there is no such subsequence,
+ * return an empty string.
+ */
+
+/**
+ * @param {string} s
+ * @param {number} k
+ * @return {string}
+ */
+var longestSubsequenceRepeatedK = function(s, k) {
+  const n = s.length;
+  const freq = new Array(26).fill(0);
+  for (const char of s) {
+    freq[char.charCodeAt(0) - 97]++;
+  }
+
+  let candidates = '';
+  for (let i = 0; i < 26; i++) {
+    const count = Math.floor(freq[i] / k);
+    candidates += String.fromCharCode(97 + i).repeat(count);
+  }
+
+  function canFormSubsequence(seq) {
+    let j = 0;
+    for (let i = 0; i < n && j < seq.length * k; i++) {
+      if (s[i] === seq[j % seq.length]) j++;
+    }
+    return j >= seq.length * k;
+  }
+
+  let result = '';
+  backtrack('', candidates);
+  return result;
+
+  function backtrack(curr, remaining) {
+    if (curr.length > result.length || (curr.length === result.length && curr > result)) {
+      if (canFormSubsequence(curr)) result = curr;
+    }
+    if (!remaining) return;
+
+    for (let i = remaining.length - 1; i >= 0; i--) {
+      const nextChar = remaining[i];
+      backtrack(curr + nextChar, remaining.slice(0, i) + remaining.slice(i + 1));
+    }
+  }
+};