leetcode-20 有效的括号

/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function (s) {
  const map = {
    "(": ")",
    "[": "]",
    "{": "}",
  };
  const stack = [];
  for (let i = 0; i < s.length; i++) {
    const top = stack.length > 0 ? stack[stack.length - 1] : "";
    const cur = s[i];
    if (cur === map[top]) {
      stack.pop();
    } else {
      stack.push(cur);
    }
  }
  return stack.length === 0;
};