# LeetCode – Valid Parentheses
Date: 2019-07-19


# 题目：

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

An input string is valid if:

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

Note that an empty string is also considered valid.

**Example 1:**

```
Input: "()"
Output: true

```

**Example 2:**

```
Input: "()[]{}"
Output: true

```

**Example 3:**

```
Input: "(]"
Output: false

```

**Example 4:**

```
Input: "([)]"
Output: false

```

**Example 5:**

```
Input: "{[]}"
Output: true
```

# 解题：

      创建栈， 遇到左括号'(''\[''{' 将其入栈， 遇到右括号')''\]''}' ,   判断栈顶是不是对应的左括号， 对应出栈， 否则返回失败， 循环完毕后，判断栈是否为空，空则表示完全匹配。

# 实现：

```
class Solution {
public:
    bool isValid(string s) {
        stack<char>  ss;
        for (int i=0; i<s.size(); i++){
            if (s[i] == '(' || s[i] == '[' || s[i] == '{') {
                ss.push(s[i]);
            }
            else{
                if (ss.empty()) return false;
                if (s[i] == ')' && ss.top() != '(') return false;
                if (s[i] == ']' && ss.top() != '[') return false;
                if (s[i] == '}' && ss.top() != '{') return false;
                ss.pop();
                    
            }
        }
        return ss.empty();
    }
};
```