Add solution #516

Author: JoshCrozier

README.md

@@ -412,6 +412,7 @@
 513|[Find Bottom Left Tree Value](./0513-find-bottom-left-tree-value.js)|Medium|
 514|[Freedom Trail](./0514-freedom-trail.js)|Hard|
 515|[Find Largest Value in Each Tree Row](./0515-find-largest-value-in-each-tree-row.js)|Medium|
+516|[Longest Palindromic Subsequence](./0516-longest-palindromic-subsequence.js)|Medium|
 520|[Detect Capital](./0520-detect-capital.js)|Easy|
 521|[Longest Uncommon Subsequence I](./0521-longest-uncommon-subsequence-i.js)|Easy|
 530|[Minimum Absolute Difference in BST](./0530-minimum-absolute-difference-in-bst.js)|Easy|

solutions/0516-longest-palindromic-subsequence.js

@@ -0,0 +1,36 @@
+/**
+ * 516. Longest Palindromic Subsequence
+ * https://leetcode.com/problems/longest-palindromic-subsequence/
+ * Difficulty: Medium
+ *
+ * Given a string s, find the longest palindromic subsequence's length in s.
+ *
+ * A subsequence is a sequence that can be derived from another sequence by deleting some
+ * or no elements without changing the order of the remaining elements.
+ */
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var longestPalindromeSubseq = function(s) {
+  const dp = new Array(s.length).fill(0);
+
+  for (let i = s.length - 1, previous; i >= 0; i--) {
+    previous = dp.slice();
+    dp[i] = 1;
+    for (let j = i + 1; j < s.length; j++) {
+      if (s[i] === s[j]) {
+        dp[j] = (previous[j - 1] || 0) + 2;
+      } else {
+        dp[j] = Math.max(dp[j - 1], previous[j]);
+      }
+    }
+  }
+
+  return dp[s.length - 1];
+};