1021. Remove Outermost Parentheses.js

// A valid parentheses string is either empty "", "(" + A + ")", or A + B, where A and B are valid parentheses strings, and + represents string concatenation.

// For example, "", "()", "(())()", and "(()(()))" are all valid parentheses strings.
// A valid parentheses string s is primitive if it is nonempty, and there does not exist a way to split it into s = A + B, with A and B nonempty valid parentheses strings.

// Given a valid parentheses string s, consider its primitive decomposition: s = P1 + P2 + ... + Pk, where Pi are primitive valid parentheses strings.

// Return s after removing the outermost parentheses of every primitive string in the primitive decomposition of s.

// Example 1:

// Input: s = "(()())(())"
// Output: "()()()"
// Explanation:
// The input string is "(()())(())", with primitive decomposition "(()())" + "(())".
// After removing outer parentheses of each part, this is "()()" + "()" = "()()()".
// Example 2:

// Input: s = "(()())(())(()(()))"
// Output: "()()()()(())"
// Explanation:
// The input string is "(()())(())(()(()))", with primitive decomposition "(()())" + "(())" + "(()(()))".
// After removing outer parentheses of each part, this is "()()" + "()" + "()(())" = "()()()()(())".
// Example 3:

// Input: s = "()()"
// Output: ""
// Explanation:
// The input string is "()()", with primitive decomposition "()" + "()".
// After removing outer parentheses of each part, this is "" + "" = "".

const removeOuterParentheses = s => {
	let result = ''
	let level = 0

	for (const item of s) {
		if (item === ')') {
			level--
		}
		if (level >= 1) {
			result += item
		}
		if (item === '(') {
			level++
		}
	}
	return result
}