May 29, 2019 · Coding Challenge JavaScript

Remove Outermost Parentheses

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 = P_1 + P_2 + ... + P_k, where P_i 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: "(()())(())"
Output: "()()()"
Explanation: 
The input string is "(()())(())", with primitive decomposition "(()())" + "(())".
After removing outer parentheses of each part, this is "()()" + "()" = "()()()".

Example 2:

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

Example 3:

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

Note:

S.length <= 10000
S[i] is "(" or ")"
S is a valid parentheses string

Solution

/**
 * @param {string} S
 * @return {string}
 * @time complexity: O(n) where n is the length of S
 * @space complexity: O(n)
 */
var removeOuterParentheses = function(S) {
  let bal = 0;
  let res = '';

  for (let i = 0; i < S.length; i++) {
    if (S.charAt(i) === '(') {
      if (bal !== 0) {
        res += S.charAt(i);
      }
      bal++;
    } else {
      if (bal !== 1) {
        res += S.charAt(i);
      }
      bal--;
    }
  }

  return res;
};

Test Case

const assert = require('chai').assert;

describe('Remove Outermost Parentheses', () => {

  it('should return \'()()()\' when \'(()())(())\' is given', () => {
    assert.strictEqual(removeOuterParentheses('(()())(())'), '()()()');
  });

  it('should return \'()()()\' when \'(()())(())(()(()))\' is given', () => {
    assert.strictEqual(removeOuterParentheses('(()())(())(()(()))'), '()()()()(())');
  });

  it('should return \'\' when \'()()\' is given', () => {
    assert.strictEqual(removeOuterParentheses('()()'), '');
  });

});
  Remove Outermost Parentheses
    ✓ should return '()()()' when '(()())(())' is given
    ✓ should return '()()()' when '(()())(())(()(()))' is given
    ✓ should return '' when '()()' is given


  3 passing (15ms)



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