JavaScript算法试题系列-07

问题描述：

// 判断大括号是否闭合创建一个函数来判断给定的表达式中的大括号是否闭合：
var expression = "{{}}{}{}";
var expressionFalse = "{}{{}";

isBalanced(expression); // true
isBalanced(expressionFalse); // false
isBalanced(""); // true

解答：

function isBalanced(expression) {
  var checkString = expression;
  var stack = [];

  // If empty, parentheses are technically balanced
  if (checkString.length <= 0) return true;

  for (var i = 0; i < checkString.length; i++) {
    if(checkString[i] === '{') {
      stack.push(checkString[i]);
    } else if (checkString[i] === '}') {
      // Pop on an empty array is undefined
      if (stack.length > 0) {
        stack.pop();
      } else {
        return false;
      }
    }
  }

  // If the array is not empty, it is not balanced
  if (stack.pop()) return false;
  return true;
}