Merge pull request #102 from Joshua-Lu/patch-19

添加 0104.二叉树的最大深度 Java版本 递归法与迭代法

problems/0104.二叉树的最大深度.md

@@ -231,19 +231,53 @@ public:
 
 
 Java：
-```java
+
+```Java
 class Solution {
+    /**
+     * 递归法
+     */
     public int maxDepth(TreeNode root) {
         if (root == null) {
             return 0;
         }
-        int leftdeep = maxDepth(root.left);
-        int rightdeep = maxDepth(root.right);
-        return 1+Math.max(leftdeep,rightdeep);
+        int leftDepth = maxDepth(root.left);
+        int rightDepth = maxDepth(root.right);
+        return Math.max(leftDepth, rightDepth) + 1;
+
     }
 }
 ```
 
+```Java
+class Solution {
+    /**
+     * 迭代法，使用层序遍历
+     */
+    public int maxDepth(TreeNode root) {
+        if(root == null) {
+            return 0;
+        }
+        Deque<TreeNode> deque = new LinkedList<>();
+        deque.offer(root);
+        int depth = 0;
+        while (!deque.isEmpty()) {
+            int size = deque.size();
+            depth++;
+            for (int i = 0; i < size; i++) {
+                TreeNode poll = deque.poll();
+                if (poll.left != null) {
+                    deque.offer(poll.left);
+                }
+                if (poll.right != null) {
+                    deque.offer(poll.right);
+                }
+            }
+        }
+        return depth;
+    }
+}
+```
 
 Python：