add js soultion for leetcode 20

Author: swiftwind0405

README.md

@@ -392,7 +392,7 @@ LeetCode
 |23|[Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/)| |Hard|
 |22|[Generate Parentheses](https://leetcode.com/problems/generate-parentheses/)| [js](./algorithms/generateParentheses/generateParentheses.js) |Medium|
 |21|[Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)| [java](./algorithm/mergeTwoSortedLists/Solution.java) |Easy|
-|20|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)| |Easy|
+|20|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)| [js](./algorithms/validParentheses/validParentheses.js) |Easy|
 |19|[Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/)| [js](./algorithms/removeNthNodeFromEndOfList/removeNthNodeFromEndOfList.js) |Easy|
 |18|[4Sum](https://leetcode.com/problems/4sum/)| [js](./algorithms/4Sum/4Sum.js) |Medium|
 |17|[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)| |Medium|

algorithms/validParentheses/validParentheses.js

@@ -0,0 +1,20 @@
+var isValid = function(s) {
+    const stack = [], map = {
+        ")": "(",
+        "]": "[",
+        "}": "{",
+
+    };
+    for (str of s) {
+        if (str => ["(", "[", "{"].includes(str)) {
+            stack.push(str)
+        } else {
+            if (stack[stack.length - 1] === map[str]) {
+                stack.pop();
+            } else {
+                return false;
+            }
+        }
+    }
+    return stack.length === 0;
+};