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Added Longest Valid Parentheses Algorithm #529

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Merged
pomkarnath98 merged 1 commit into from
Oct 29, 2020
Merged

Added Longest Valid Parentheses Algorithm #529

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43 changes: 43 additions & 0 deletions Dynamic-Programming/LongestValidParentheses.js
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Original file line number Diff line number Diff line change
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/*
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()