add 637

Author: awesomelike

easy/637-average-levels-binary-tree.java

@@ -0,0 +1,51 @@
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.LinkedList;
+import java.util.Queue;
+
+class TreeNode {
+  int val;
+  TreeNode left;
+  TreeNode right;
+  TreeNode() {}
+  TreeNode(int val) { this.val = val; }
+    TreeNode(int val, TreeNode left, TreeNode right) {
+      this.val = val;
+      this.left = left;
+      this.right = right;
+    }
+  }
+
+  class Solution {
+    public List<Double> averageOfLevels(TreeNode root) {
+      if (root == null) {
+        return Collections.emptyList();
+      }
+      List<Double> answer = new ArrayList<Double>();
+      
+      double sum = 0;
+      Queue<TreeNode> queue = new LinkedList<TreeNode>();
+      queue.add(root);
+      
+      while(!queue.isEmpty()) {
+        int size = queue.size();
+  
+        for (int i=0; i<size; i++) {
+          TreeNode node = queue.poll();
+          sum += node.val;
+  
+          if (node.left != null) {
+            queue.add(node.left);
+          }
+          if (node.right != null) {
+            queue.add(node.right);
+          }
+        }
+        answer.add(sum / size);
+        sum = 0;
+      }
+  
+      return answer;
+    }
+  }