# 有效的括号

<p>给定一个只包括 <code>'('</code>，<code>')'</code>，<code>'{'</code>，<code>'}'</code>，<code>'['</code>，<code>']'</code> 的字符串 <code>s</code> ，判断字符串是否有效。</p><p>有效字符串需满足：</p><ol>	<li>左括号必须用相同类型的右括号闭合。</li>	<li>左括号必须以正确的顺序闭合。</li></ol><p> </p><p><strong>示例 1：</strong></p><pre><strong>输入：</strong>s = "()"<strong><br />输出：</strong>true</pre><p><strong>示例 2：</strong></p><pre><strong>输入：</strong>s = "()[]{}"<strong><br />输出：</strong>true</pre><p><strong>示例 3：</strong></p><pre><strong>输入：</strong>s = "(]"<strong><br />输出：</strong>false</pre><p><strong>示例 4：</strong></p><pre><strong>输入：</strong>s = "([)]"<strong><br />输出：</strong>false</pre><p><strong>示例 5：</strong></p><pre><strong>输入：</strong>s = "{[]}"<strong><br />输出：</strong>true</pre><p> </p><p><strong>提示：</strong></p><ul>	<li><code>1 <= s.length <= 10<sup>4</sup></code></li>	<li><code>s</code> 仅由括号 <code>'()[]{}'</code> 组成</li></ul>
<p>以下<span style="color:red">错误</span>的选项是？</p>

## aop

### before

```c
#include <bits/stdc++.h>
using namespace std;
```

### after

```c
int main()
{
    Solution sol;
    string s = "([)]";
    bool res;

    res = sol.isValid(s);
    cout << res;
    return 0;
}
```

## 答案

```c
class Solution
{
public:
    bool isValid(string s)
    {
        stack<char> symbols;
        for (int i = 0; i < s.size(); i++)
        {
            if (s[i] == '(' || s[i] == '[' || s[i] == '{')
                symbols.push(s[i + 1]);
            else
            {
                if (symbols.size() == 0)
                    return false;

                char match;
                if (s[i] == ')')
                    match = '(';
                else if (s[i] == ']')
                    match = '[';
                else if (s[i] == '}')
                    match = '{';
                char c = symbols.top();
                symbols.pop();

                if (c != match)
                    return false;
            }
        }
        if (symbols.size() != 0)
            return false;

        return true;
    }
};
```
## 选项


### A

```c
class Solution
{
public:
    bool isValid(string s)
    {
        if (s.size() % 2 != 0)
            return false;
        if (s.size() == 0)
            return true;

        string temp;
        temp.push_back(s[0]);
        for (int i = 1; i < s.size(); ++i)
        {
            int k = temp.size() - 1;
            if (temp[k] == '(' && s[i] == ')')
                temp.pop_back();
            else if (temp[k] == '[' && s[i] == ']')
                temp.pop_back();
            else if (temp[k] == '{' && s[i] == '}')
                temp.pop_back();
            else
                temp.push_back(s[i]);
        }
        return temp.size() == 0;
    }
};
```

### B

```c
class Solution
{
public:
    bool isValid(string s)
    {
        if (s.length() == 0)
        {
            return true;
        }
        if (s.length() % 2 != 0)
        {
            return false;
        }
        stack<char> st;
        for (auto item : s)
        {
            if (item == '(' || item == '[' || item == '{')
                st.push(item);
            if (st.empty())
                return false;
            if (item == ')')
            {
                if (st.top() == '(')
                {
                    st.pop();
                }
                else
                    return false;
            }
            else if (item == ']')
            {
                if (st.top() == '[')
                {
                    st.pop();
                }
                else
                    return false;
            }
            else if (item == '}')
            {
                if (st.top() == '{')
                {
                    st.pop();
                }
                else
                    return false;
            }
        }
        return st.empty();
    }
};
```

### C

```c
class Solution
{
public:
    bool isValid(string s)
    {
        stack<char> data;
        map<char, char> match = {{'{', '}'}, {'[', ']'}, {'(', ')'}};
        for (auto &i : s)
        {
            if (i == '(' || i == '[' || i == '{')
            {
                /* code */
                data.push(i);
            }
            else
            {
                if (data.empty())
                    return false;
                char top = data.top();
                data.pop();
                if (match[top] != i)
                    return false;
            }
        }
        return data.size() == 0;
    }
};
```
