题解 | #最长的括号子串#

  * 
  * @param s string字符串 
  * @return int整型
  */
function longestValidParentheses( s ) {
    // write code here
     let ls = 0, rs = 0;
     let n = s.length;
     let ans = 0;
     for(let i = 0; i < n; i ++){ //正序遍历一遍
        if(s[i] == '(')
            ls++;
        else
            rs++;
        if(ls == rs)
            ans = Math.max(ans, ls * 2); //如果左括号与右括号数量相等则说明当前序列是合法的并更新答案
        else if(rs > ls)
            ls = rs = 0;
    }
    ls = rs = 0;
    for(let i = n - 1; i >= 0; i --){    //逆序遍历一遍
        if(s[i] == '(') ls ++;
        else rs ++;
        if(ls == rs) ans = Math.max(ans, ls * 2);   //与正序一致
        else if(rs < ls) ls = rs = 0;
    }
    return ans;
}
module.exports = {
    longestValidParentheses : longestValidParentheses
};