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  • leetcode — longest-valid-parentheses

    import java.util.Stack;
    
    /**
     * Source : https://oj.leetcode.com/problems/longest-valid-parentheses/
     *
     * Created by lverpeng on 2017/7/13.
     *
     * 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 LongestParentheses {
    
        /**
         * 最长有效的括号字符串
         *
         * 和之前判断括号匹配的一样使用栈,因为要计算长度,所以栈里面放括号字符的序号
         *
         * 边界情况:
         * 栈为空遇到了右括号,开始压入一个-1,遇到右括号换的时候出栈,并压入新的右括号的序号
         *
         * @param parentheseStr
         * @return
         */
        public int longestParentheses (String parentheseStr) {
            Stack<Integer> stack = new Stack<Integer>();
            int maxLen = 0;
            stack.push(-1);
            for (int i = 0; i < parentheseStr.length(); i++) {
                if (parentheseStr.charAt(i) == '(') {
                    stack.push(i);
                } else {
                    if (stack.size() > 1) {
                        stack.pop();
                        int temp = stack.peek();
                        if (maxLen < (i - temp)) {
                            maxLen = i - temp;
                        }
                    } else {
                        stack.pop();
                        stack.push(i);
                    }
                }
            }
            return maxLen;
        }
    
    
        public static void main(String[] args) {
            LongestParentheses longestParentheses = new LongestParentheses();
            System.out.println(longestParentheses.longestParentheses("(()"));
            System.out.println(longestParentheses.longestParentheses(")()())"));
        }
    }
    
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  • 原文地址:https://www.cnblogs.com/sunshine-2015/p/7440059.html
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