Java/DynamicProgramming/LongestValidParentheses.java at master · oribach/Java · GitHub

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package DynamicProgramming;

import java.util.Scanner;

/**

* Given a string containing just the characters '(' and ')', find the length of the longest valid

* (well-formed) parentheses substring.

* @author Libin Yang (https://github.com/yanglbme)

* @since 2018/10/5

public class LongestValidParentheses {

public static int getLongestValidParentheses(String s) {

if (s == null || s.length() < 2) {

return 0;

}

char[] chars = s.toCharArray();

int n = chars.length;

int[] res = new int[n];

res[0] = 0;

res[1] = chars[1] == ')' && chars[0] == '(' ? 2 : 0;

int max = res[1];

for (int i = 2; i < n; ++i) {

if (chars[i] == ')') {

if (chars[i - 1] == '(') {

res[i] = res[i - 2] + 2;

} else {

int index = i - res[i - 1] - 1;

if (index >= 0 && chars[index] == '(') {

// ()(())

res[i] = res[i - 1] + 2 + (index - 1 >= 0 ? res[index - 1] : 0);

}

max = Math.max(max, res[i]);

}

return max;

}

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);

while (true) {

String str = sc.nextLine();

if ("quit".equals(str)) {

break;

}

System.out.println("Len is: " + getLongestValidParentheses(str));

}

sc.close();

}

Java/DynamicProgramming/LongestValidParentheses.java at master · oribach/Java · GitHub

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