Longest Valid Parentheses

最新推荐文章于 2019-10-09 18:26:29 发布

原创最新推荐文章于 2019-10-09 18:26:29 发布 · 671 阅读

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本文介绍了一种求解字符串中最长有效括号子串长度的方法。通过两次遍历，分别从左到右和从右到左计算有效的括号对数，找出最长的有效括号子串长度。

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.

public class Solution {
	public static void main(String[] args) {
		System.out.println( longestValidParentheses("()"));
	}
	
    public static int longestValidParentheses(String str) {
    	if (str == null || str.length() == 0) return 0;
        int max = 0;
	    int total = 0;
	    int numberofLeftParentheses = 0;
	    for (int k = 0; k < str.length(); k++) {
	        if (str.charAt(k) == '(') {
	        	numberofLeftParentheses++;
	        	total++;
	        } else {
	        	numberofLeftParentheses--;
	        	total++;
	        }
	        
	        if (numberofLeftParentheses == 0 && max < total) {
	        	max = total;
	        }
	        
	        if (numberofLeftParentheses < 0) {
	        	total = 0;
	        	numberofLeftParentheses = 0;
	        }
	    }
	   
        total = 0;
        numberofLeftParentheses = 0;
	    for (int k = str.length() - 1; k >= 0; k--) {
	        if (str.charAt(k) == ')') {
	        	numberofLeftParentheses++;
	        	total++;
	        } else {
	        	numberofLeftParentheses--;
	        	total++;
	        }
	        
	        if (numberofLeftParentheses == 0 && max < total) {
	        	max = total;
	        }
	        
	        if (numberofLeftParentheses < 0) {
	        	total = 0;
	        	numberofLeftParentheses = 0;
	        }
	    }
        return max;
    }
    
 // this method will return total number of valid pare of parentheses (not continuous). 
	public static int totalValidPairOfParentheses(String str) {
	    if (str == null || str.length() == 0) return 0;
	    int total = 0;
	    int numberofLeftParentheses = 0;
	    for (int k = 0; k < str.length(); k++) {
	        if (str.charAt(k) == '(') {
	        	numberofLeftParentheses++;
	        } else {
	            if (numberofLeftParentheses > 0) {
	            	numberofLeftParentheses--;
	                total++;
	            }
	        }
	    }
	    return total;
	}
}