From f856bcfef005fc54d2e55d3e811731ce0f35257b Mon Sep 17 00:00:00 2001
From: Joshua <47053655+Joshua-Lu@users.noreply.github.com>
Date: Fri, 14 May 2021 01:02:55 +0800
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添加 0222.完全二叉树的节点个数 Java版本，2种解法
---
 .../0222.完全二叉树的节点个数.md    | 42 +++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/problems/0222.完全二叉树的节点个数.md b/problems/0222.完全二叉树的节点个数.md
index 367fa717..64705ed6 100644
--- a/problems/0222.完全二叉树的节点个数.md
+++ b/problems/0222.完全二叉树的节点个数.md
@@ -194,7 +194,49 @@ public:
 
 
 Java：
+```java
+class Solution {
+    // 通用递归解法
+    public int countNodes(TreeNode root) {
+        if(root == null) {
+            return 0;
+        }
+        return countNodes(root.left) + countNodes(root.right) + 1;
+    }
+}
+```
 
+```java
+class Solution {
+    /**
+     * 针对完全二叉树的解法
+     *
+     * 满二叉树的结点数为：2^depth - 1
+     */
+    public int countNodes(TreeNode root) {
+        if(root == null) {
+            return 0;
+        }
+        int leftDepth = getDepth(root.left);
+        int rightDepth = getDepth(root.right);
+        if (leftDepth == rightDepth) {// 左子树是满二叉树
+            // 2^leftDepth其实是 （2^leftDepth - 1） + 1 ，左子树 + 根结点
+            return (1 << leftDepth) + countNodes(root.right);
+        } else {// 右子树是满二叉树
+            return (1 << rightDepth) + countNodes(root.left);
+        }
+    }
+
+    private int getDepth(TreeNode root) {
+        int depth = 0;
+        while (root != null) {
+            root = root.left;
+            depth++;
+        }
+        return depth;
+    }
+}
+```
 
 Python：