add the solution for lettcode 242

Author: swiftwind0405

README.md

@@ -186,7 +186,7 @@ LeetCode
 |260|[Single Number III](https://leetcode.com/problems/single-number-iii/)| |Medium|
 |258|[Add Digits](https://leetcode.com/problems/add-digits/)| |Easy|
 |257|[Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/)| |Easy|
-|242|[Valid Anagram](https://leetcode.com/problems/valid-anagram/)| |Easy|
+|242|[Valid Anagram](https://leetcode.com/problems/valid-anagram/)| [js](./algorithms/validAnagram/validAnagram.js) |Easy|
 |241|[Different Ways to Add Parentheses](https://leetcode.com/problems/different-ways-to-add-parentheses/)||Medium|
 |240|[Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/)||Medium|
 |239|[Sliding Window Maximum](https://leetcode.com/problems/sliding-window-maximum/)| |Hard|

algorithms/validAnagram/validAnagram.js

@@ -0,0 +1,38 @@
+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {boolean}
+ */
+var isAnagram = function(s, t) {
+    const map1 = new Map();
+    const map2 = new Map();
+
+    function countNum(str, map) {
+        for (let i = 0; i < str.length; i++) {
+            const current = str[i]
+            const value = map.get(current);
+            if (value) {
+                map.set(current, value + 1)
+            } else {
+                map.set(current, 1)
+            }
+        }
+    }
+
+    countNum(s, map1);
+    countNum(t, map2);
+
+    if (map1.size !== map2.size || (
+        [...map1.keys()].sort().join("") !== [...map2.keys()].sort().join("")
+    )) {
+        return false;
+    }
+
+    for(let [key, value] of map1) {
+        if (value !== map2.get(key)) {
+            return false;
+        }
+    }
+
+    return true;    
+};