Offer_32 最长有效括号

给你一个只包含 '(' 和 ')' 的字符串，找出最长有效（格式正确且连续）括号子串的长度。

 

package com.lhb.offer;

import java.util.Deque;
import java.util.LinkedList;

/**
 * @author lhb
 * @date 2022/3/15
 */
public class Offer_32 {
    // stack
    static int solution_1(String s) {
        int ret = 0;
        Deque<Integer> st = new LinkedList<>();
        st.push(-1);
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '(') {
                st.push(i);
            } else {
                st.pop();
                if (st.isEmpty()) {
                    st.push(i);
                } else {
                    ret = Math.max(ret, i - st.peek());
                }
            }
        }
        return ret;
    }
    // dp
    static int solution_2 (String s) {
        int[] dp = new int[s.length()];
        int ret = 0;
        for (int i = 1; i < s.length(); i++) {
            if (s.charAt(i) == ')') {
                if ( s.charAt(i - 1) == '(') {
                    dp[i] = (i >= 2) ? dp[i - 2] + 2 : 2;
                } else if (i - dp[i - 1] > 0 && s.charAt(i - dp[i - 1] - 1) == '(') {
                    dp[i] = dp[i - 1] + ((i - dp[i - 1]) >= 2 ? dp[i - dp[i - 1] - 2] : 0) + 2;
                }
            }
            ret = Math.max(ret, dp[i]);
        }
        return ret;
    }
    // left right
    static int solution_3(String s) {
        int left = 0;
        int right = 0;
        int ret =0;
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == ')') {
                right++;
            }else {
                left++;
            }
            if (left == right) {
                ret = Math.max(ret, 2 * right);
            } else if (right > left) {
                left =right = 0;
            }
        }
        left = right = 0;
        for (int i = s.length() - 1; i >= 0; i--) {
            if (s.charAt(i) == ')') {
                right++;
            }else {
                left++;
            }
            if (left == right) {
                ret = Math.max(ret, 2 * right);
            } else if (right < left) {
                left = right = 0;
            }
        }
        return ret;
    }
    public static void main(String[] args) {
        System.out.println(solution_1("(((()))))(()()()))))")); // 8
        System.out.println(solution_2("(((()))))(()()()))))"));// 8
        System.out.println(solution_3("(((()))))(()()()))))")); // 8
    }
}