Q.

Description:
Write a function that takes a string of parentheses, and determines if the order of the parentheses is valid. The function should return true if the string is valid, and false if it's invalid.

Examples
"()" => true
")(()))" => false
"(" => false
"(())((()())())" => true
Constraints
0 <= input.length <= 100

A)

function validParentheses(parens){
  //TODO 
  let count = 0;
  for (let i = 0; i < parens.length; i++) {
    if (parens[i] === '(') count++
    else count--
    if (count < 0) return false
  }
  return count === 0 ? true : false
}

이렇게 쉬운문제가 왜 5kyu에 있지? 하고 풀어봤는데 edge case를 생각하기까지 30분이나 걸렸다.