Update README.md

Author: ravhb

Algorithms/Most Frequent Subtree Sum/README.md

@@ -5,4 +5,46 @@
 
 
 ```js
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number[]}
+ */
+function getSum (root, map) {
+    if (root === null) return 0;
+    var left = getSum(root.left, map);
+    var right = getSum(root.right, map);
+    var sum = root.val + left + right;
+    
+    map[sum] === undefined ? map[sum] = 1 : map[sum]++;
+    return sum;
+}
+var findFrequentTreeSum = function(root) {
+    if (root === null) return [];
+    var valueCountMap = {};
+    var max = -1;
+    var ret = [];
+    var key;
+    
+    getSum(root, valueCountMap);
+    for (key in valueCountMap) {
+        if (valueCountMap[key] > max) {
+            max = valueCountMap[key];
+        }
+    }
+    
+    for (key in valueCountMap) {
+        if (valueCountMap[key] === max) {
+            ret.push(parseInt(key));
+        }
+    }
+    
+    return ret;
+};
 ```