Leetcode Longest Valid Parentheses report, validparentheses

Source: Internet
Author: User

Leetcode Longest Valid Parentheses report, validparentheses
Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.
For "()", the longest valid parentheses substring is "()", which has length = 2.
Another example is ") ()", where the longest valid parentheses substring is "()", which has length = 4.
Https://oj.leetcode.com/problems/longest-valid-parentheses/
Analyze and obtain the length of the valid () pair in a string consisting of '(' and. For example: (), the result is 4. () The result is 6. () The result is 4.
Solution: the easiest way to solve the problem is to calculate the number of valid () strings between any two points (I to j). The results can be obtained through dynamic planning. Algorithm complexity:
To solve the problem of O (n), you need to understand the following situations:

The AC code is as follows:

`public class Solution {    public int longestValidParentheses(String s) {        if(s==null||s.length()==0) {            return 0;        }        int start     = -1;        int maxLength = 0;        Stack stack   = new Stack();        for(int i=0;i<s.length();i++) {            if(s.charAt(i)=='(') {                stack.push(i);            } else {                if(!stack.empty()) {                    stack.pop();                    if(stack.empty()==true) {                        maxLength = Math.max(i - start , maxLength);                    } else {                        maxLength = Math.max(i - (int)stack.peek() , maxLength);                    }                } else {                    start = i;                }            }        }            return maxLength;    }}`

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