题目：

题解：

func longestValidParentheses(s string) int {left, right, maxLength := 0, 0, 0for i := 0; i < len(s); i++ {if s[i] == '(' {left++} else {right++}if left == right {maxLength = max(maxLength, 2 * right)} else if right > left {left, right = 0, 0}}left, right = 0, 0for i := len(s) - 1; i >= 0; i-- {if s[i] == '(' {left++} else {right++}if left == right {maxLength = max(maxLength, 2 * left)} else if left > right {left, right = 0, 0}}return maxLength
}func max(x, y int) int {if x > y {return x}return y
}