[32] 最长有效括号

/**
 * @param {string} s
 * @return {number}
 */
var longestValidParentheses = function (s) {
  let [max, left, right] = [0, 0, 0];
  for (let i = 0; i < s.length; i++) {
    if (s[i] == "(") {
      left += 1;
    } else {
      right += 1;
    }
    if (left == right) {
      max = max < 2 * right ? 2 * right : max;
    } else if (left < right) {
      right = 0;
      left = 0;
    }
  }
  //一定要注意清空哦
  right = 0;
  left = 0;

  for (let i = s.length - 1; i >= 0; i--) {
    if (s[i] === "(") {
      left += 1;
    } else {
      right += 1;
    }
    if (left == right) {
      max = max < 2 * right ? 2 * right : max;
    } else if (left > right) {
      right = 0;
      left = 0;
    }
  }
  return max;
};