leetcode之Valid Parentheses

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于 2018-09-30 16:36:09 发布

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分类专栏： leetcode和机试题文章标签： leetcode

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本文介绍了一种使用栈和映射表来验证字符串中括号是否正确配对的算法。该算法通过遍历输入字符串，利用栈来跟踪左括号，并使用映射表来检查右括号是否与最近的左括号类型相匹配。文章提供了完整的C++代码实现，展示了如何判断一个包含括号的字符串是否有效。

题目：

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.

Note that an empty string is also considered valid.

代码：

#include<iostream>
#include<set>
#include<map>
#include<stack>
using namespace std;

bool isValid(string s) {

	int len = s.size();
	if (len == 0)return true;
	if (len % 2 != 0)return false;
	stack<char> cstack;
	map<char, char> m;
	m['('] = ')';
	m['{'] = '}';
	m['['] = ']';
	set<char> left = { '(','{','[' };
	if (!left.count(s[0]))return false;
	cstack.push(s[0]); char last = s[0];

	for (int i = 1; i < len; i++) {
		if (left.count(s[i])) {
			cstack.push(s[i]);
			last = s[i]; }
		else if (s[i] == m[last]) { 
			cstack.pop(); 
			if (cstack.size() == 0)last='0';
			else last = cstack.top(); }
		else return false;
	}

	if (cstack.size() != 0)return false;
	return true;
}
int  main() {
	string s = "()[]{}";
	bool m = isValid(s);
	cout << m << endl;

	return 0;
}