# 020. Valid Parentheses

## 刷题内容

• https://leetcode.com/problems/two-sum

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.


#### 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


## 解题方案

/**
* @param {string} s
* @return {boolean}
*/
var isValid = function(s) {
if(!s){
return true;
}
let array = [];
for(let i = 0,len = s.length; i<len; i++){
let cur = s.charAt(i);
if(cur === '(' || cur === '{' || cur === '['){
array.push(cur);
}else if(!array.length){
return false;
}else{
let pre = array.pop();
if(pre === '(' && cur !== ')'){
return false;
}
if(pre === '{' && cur !== '}'){
return false;
}
if(pre === '[' && cur !== ']'){
return false;
}
}
}
return !array.length
};


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