leetcode 括号类型题解

参考宫水三叶题解，非常有启发意义https://leetcode.cn/problems/valid-parenthesis-string/solutions/992601/gong-shui-san-xie-yi-ti-shuang-jie-dong-801rq/

32. 最长有效括号

使用栈+一次遍历，巧妙得出最长有效括号长度

func longestValidParentheses(s string) int {
    stack := make([]int,0)
    stack =append(stack,-1)
    mx := 0 
    for i:=0;i<len(s);i++{
        if s[i]=='('{
            stack = append(stack,i)
        }else{
            stack = stack[:len(stack)-1]
            if len(stack) == 0 {
                stack =append(stack,i)
            }else{
                mx  =max(mx,i-stack[len(stack)-1])
            }
        }
    }

    return mx
}