validParenthese

README.md

@@ -2,6 +2,8 @@
 leetcode题解，记录自己的leecode解题之路。
 
 ## 传送门
+### 简单难度
+- [20. Valid Parentheses](https://github.com/azl397985856/leetcode/blob/master/validParentheses.md)
 ### 中等难度
 - [2. Add Two Numbers](https://github.com/azl397985856/leetcode/blob/master/addTwoNumbers.md)
 - [3. Longest Substring Without Repeating Characters](https://github.com/azl397985856/leetcode/blob/master/longestSubstringWithoutRepeatingCharacters.md)

validParentheses.md

+## 题目地址
+https://leetcode.com/problems/valid-parentheses/description
+
+## 题目描述
+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
+
+
+## 思路
+
+使用栈,遍历输入字符串
+
+如果当前字符为左半边括号时，则将其压入栈中
+
+如果遇到右半边括号时，分类讨论：
+
+1）如栈不为空且为对应的左半边括号，则取出栈顶元素，继续循环  
+
+2）若此时栈为空，则直接返回false
+
+3）若不为对应的左半边括号，反之返回false
+
+
+
+![20.validParentheses](./assets/20.validParentheses.gif)
+
+(图片来自： https://github.com/MisterBooo/LeetCodeAnimation)
+
+## 关键点解析
+
+1. 栈的基本特点和操作
+2. 如果你用的是JS没有现成的栈，可以用数组来模拟
+入： push  出:  pop
+
+> 入： push  出 shift 就是队列
+## 代码
+
+
+```js
+/*
+ * @lc app=leetcode id=20 lang=javascript
+ *
+ * [20] Valid Parentheses
+ *
+ * https://leetcode.com/problems/valid-parentheses/description/
+ *
+ * algorithms
+ * Easy (35.97%)
+ * Total Accepted:    530.2K
+ * Total Submissions: 1.5M
+ * Testcase Example:  '"()"'
+ *
+ * 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
+ * 
+ * 
+ */
+/**
+ * @param {string} s
+ * @return {boolean}
+ */
+var isValid = function(s) {
+    let valid = true;
+    const stack = [];
+    const mapper = {
+        '{': "}",
+        "[": "]",
+        "(": ")"
+    }
+    
+    for(let i in s) {
+        const v = s[i];
+        if (['(', '[', '{'].indexOf(v) > -1) {
+            stack.push(v);
+        } else {
+            const peak = stack.pop();
+            if (v !== mapper[peak]) {
+                valid = false
+            }
+        }
+    }
+
+    if (stack.length > 0) return false;
+
+    return valid;
+};
+```
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