32. Longest Valid Parentheses（js）

32. Longest Valid Parentheses

Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.

Example 1:

Input: "(()"
Output: 2
Explanation: The longest valid parentheses substring is "()"

Example 2:

Input: ")()())"
Output: 4
Explanation: The longest valid parentheses substring is "()()"
题意：求出最长的有效括号的长度
代码如下：

/**
 * @param {string} s
 * @return {number}
 */
var longestValidParentheses = function(s) {
    var stack=[];
    var res=0,start=0;
    for(var i=0;i<s.length;i++){
        if(s[i]==='('){
            stack.push(i)
        }else if(s[i]===')'){
            if(stack.length===0){
                start=i+1;
            }else{
                stack.length=stack.length-1;
                res=stack.length===0?Math.max(res,i-start+1):Math.max(res,i-stack[stack.length-1]);
            }
        }
    }
    return res;

};