## 1. Problem

Given a string s 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. Every close bracket has a corresponding open bracket of the same type.

Example 1:

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

Example 2:

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

Example 3:

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

Constraints:

- 1 <= s.length <= 104
- s consists of parentheses only ‘()[]{}’.

## 2. Solution

I solve this problem like this.

- Using stack and dictionary.
- It loops through the for string and checks each word one by one.
- If character is in ‘([{‘, push stack.
- If character is not in ‘([{‘, check stack’s top value is pair of brackets.

```
class Solution:
def isValid(self, s: str) -> bool:
stack = []
for _s in s:
if _s in '([{':
stack.append(_s)
continue
dic = {'(': ')', '[': ']', '{': '}'}
if len(stack) > 0 and dic.get(stack[-1], None) == _s:
stack.pop()
continue
else:
return False
return True if len(stack) == 0 else False
```