add 637

fishercoder1534 · fishercoder1534 · commit 212c3a523caa · 2017-07-09T11:32:59.000-07:00
diff --git a/README.md b/README.md
@@ -20,6 +20,7 @@ Your ideas/fixes/algorithms are more than welcome!
 
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
+|637|[Average of Levels in Binary Tree](https://leetcode.com/problems/average-of-levels-in-binary-tree/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_637.java) | O(n) |O(1) | Easy | 
 |634|[Find the Derangement of An Array](https://leetcode.com/problems/find-the-derangement-of-an-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_634.java) | O(n) |O(1) | Medium | Math
 |633|[Sum of Square Numbers](https://leetcode.com/problems/sum-of-square-numbers/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_633.java) | O(logn) |O(1) | Easy | Binary Search
 |628|[Maximum Product of Three Numbers](https://leetcode.com/problems/maximum-product-of-three-numbers/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_628.java) | O(nlogn) |O(1) | Easy |
diff --git a/src/main/java/com/fishercoder/solutions/_637.java b/src/main/java/com/fishercoder/solutions/_637.java
@@ -0,0 +1,57 @@
+package com.fishercoder.solutions;
+
+import com.fishercoder.common.classes.TreeNode;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+
+/**
+ * 637. Average of Levels in Binary Tree
+ *
+ Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.
+
+ Example 1:
+ Input:
+  3
+ / \
+9  20
+  /  \
+ 15   7
+
+ Output: [3, 14.5, 11]
+ Explanation:
+
+ The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].
+ Note:
+ The range of node's value is in the range of 32-bit signed integer.
+ */
+public class _637 {
+
+    public List<Double> averageOfLevels(TreeNode root) {
+        List<Double> result = new ArrayList<>();
+        if (root == null) return result;
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.offer(root);
+        while (!queue.isEmpty()) {
+            int size = queue.size();
+            double sum = 0.0;
+            for (int i = 0; i < size; i++) {
+                TreeNode curr = queue.poll();
+                if (curr != null) {
+                    sum += curr.val;
+                }
+                if (curr.left != null) {
+                    queue.offer(curr.left);
+                }
+                if (curr.right != null) {
+                    queue.offer(curr.right);
+                }
+            }
+            result.add(sum/size);
+        }
+        return result;
+    }
+
+}
