Added Longest Valid Parentheses Algorithm

Author: suhailmalik07

Dynamic-Programming/LongestValidParentheses.js

@@ -0,0 +1,43 @@
+/*
+ LeetCode -> https://leetcode.com/problems/longest-valid-parentheses/
+
+ Given a string containing just the characters '(' and ')',
+ find the length of the longest valid (well-formed) parentheses substring.
+*/
+
+const longestValidParentheses = (s) => {
+ const n = s.length
+ const stack = []
+
+ // storing results
+ const res = new Array(n).fill(-Infinity)
+
+ for (let i = 0; i < n; i++) {
+ const bracket = s[i]
+
+ if (bracket === ')' && s[stack[stack.length - 1]] === '(') {
+ res[i] = 1
+ res[stack[stack.length - 1]] = 1
+ stack.pop()
+ } else {
+ stack.push(i)
+ }
+ }
+
+ // summing all adjacent valid
+ for (let i = 1; i < n; i++) {
+ res[i] = Math.max(res[i], res[i] + res[i - 1])
+ }
+
+ // adding 0 if there are none so it will return 0 instead of -Infinity
+ res.push(0)
+ return Math.max(...res)
+}
+
+const main = () => {
+ console.log(longestValidParentheses(')()())')) // output -> 4
+ console.log(longestValidParentheses('')) // output -> 0
+ console.log(longestValidParentheses('(()')) // output -> 2
+}
+
+main()