[leetcode] 32. Longest Valid Parentheses
来源:互联网 发布:斯隆女士原型知乎 编辑:程序博客网 时间:2024/05/22 06:35
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.
这道题是找最长匹配括号对的长度,题目难度为Hard。
括号匹配的问题经常会用到栈,遍历字符串,如果当前字符是'(',将该字符下标进栈,以便后续匹配用;如果当前字符是')',根据栈顶元素进行判断,栈顶元素如果是'(',表明出现了匹配的括号对,将栈顶元素出栈,栈顶元素如果是')',表明不能构成匹配的括号对,同样将下标进栈。这样遍历完整个字符串之后,栈中剩下的元素即是不能匹配的括号位置,每两个相邻下标相减即是他们之间的匹配括号对长度,通过比较即可得出最长匹配括号对长度。这里需要注意开始和最后匹配的括号对不要漏掉了,如果最后栈空表明整个字符串都匹配括号对了。具体代码:
class Solution {public: int longestValidParentheses(string s) { int maxLen = 0; int preIdx, curIdx; stack<int> stk; for(int i=0; i<s.size(); ++i) { if(s[i] == '(' || stk.empty()) stk.push(i); else if(s[stk.top()] == '(') stk.pop(); else stk.push(i); } preIdx = s.size(); while(!stk.empty()) { curIdx = stk.top(); stk.pop(); maxLen = max(maxLen, preIdx-curIdx-1); swap(preIdx, curIdx); } maxLen = max(maxLen, preIdx); return maxLen; }};
问题应该还能够通过动态规划来解决,因为会出现类似的子问题。用len[i]表示从下表i开始的最长匹配括号对长度,分析如下:
如果s[i] == ')',len[i]为0,因为匹配的括号对不会从')'开始;
如果s[i] == '(',根据s[i+1]进行判断:
s[i+1] == '('时,如果s[i+1+len[i+1]]为')',则s[i]和s[i+1+len[i+1]]配对,所以len[i] = len[i+1] + 2 + len[i+2+len[i+1]];如果s[i+1+len[i+1]]为'(',这里len[i+1+len[i+1]]必定为0,否则len[i+1]应该包含len[i+1+len[i+1]],所以s[i]开始没有匹配的括号对,len[i] = 0。
s[i+1] == ')'时,s[i]和s[i+1]匹配,len[i] = len[i+2] + 2,此时len[i+1]为0,相当于在i+1位置有一个长度为0的匹配括号对,这样就和上面的情况相同了。
具体代码:
class Solution {public: int longestValidParentheses(string s) { int sz = s.size(); int maxLen = 0; vector<int> len(sz+1, 0); for(int i=sz-2; i>=0; --i) { if(s[i] == '(' && i+1+len[i+1] < sz && s[i+1+len[i+1]] == ')') { len[i] = len[i+1] + 2 + len[i+2+len[i+1]]; maxLen = max(maxLen, len[i]); } } return maxLen; }};
- LeetCode --- 32. Longest Valid Parentheses
- LeetCode 32.Longest Valid Parentheses
- [Leetcode] 32. Longest Valid Parentheses
- [LeetCode]32.Longest Valid Parentheses
- [leetcode]32.Longest Valid Parentheses
- leetcode 32. Longest Valid Parentheses
- leetcode 32. Longest Valid Parentheses
- LeetCode 32. Longest Valid Parentheses
- [leetcode] 32. Longest Valid Parentheses
- LeetCode 32. Longest Valid Parentheses
- LeetCode-32.Longest Valid Parentheses
- leetcode.32. Longest Valid Parentheses
- 【leetcode】32. Longest Valid Parentheses
- leetcode 32. Longest Valid Parentheses
- [LeetCode] 32. Longest Valid Parentheses
- leetcode 32. Longest Valid Parentheses
- leetcode 32.Longest Valid Parentheses
- leetcode 32. Longest Valid Parentheses
- 根据tag获取view
- netstat -i FLG含义
- [Android]获得屏幕分辨率的两种方法20160505
- jquery实现智能表单
- 按钮动画不能放到viewDidload否则没有动画效果
- [leetcode] 32. Longest Valid Parentheses
- 百度云盘真够纠结的,免费功能突然变没了,还私自上传数据
- Spring Mvc那点事---(3)Spring Mvc项目创建
- 设置TextField的placeholder属性
- 自然声音
- replacedKeyFromProperty多级映射
- git push.default设置
- 储存版本号
- Swift 2.0 String 与 Int 类型的转换