From 7bda59c0623ff7f37f0bb4d67db44eede5b05543 Mon Sep 17 00:00:00 2001
From: h2linlin <wzh443@126.com>
Date: Thu, 13 May 2021 20:52:01 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200101.=E5=AF=B9=E7=A7=B0?=
 =?UTF-8?q?=E4=BA=8C=E5=8F=89=E6=A0=91.md=20Java=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

---
 problems/0101.对称二叉树.md | 89 +++++++++++++++++++++++++++++++-
 1 file changed, 88 insertions(+), 1 deletion(-)

diff --git a/problems/0101.对称二叉树.md b/problems/0101.对称二叉树.md
index 535300af..05a67623 100644
--- a/problems/0101.对称二叉树.md
+++ b/problems/0101.对称二叉树.md
@@ -254,7 +254,94 @@ public:
 ## 其他语言版本
 
 Java：
+```java
+public class N0101 {
+    /**
+     * 解法1：DFS，递归。
+     */
+    public boolean isSymmetric2(TreeNode root) {
+        if (root == null) {
+            return false;
+        }
 
+        return compare(root.left, root.right);
+    }
+
+    private boolean compare(TreeNode left, TreeNode right) {
+        if (left == null && right == null) {
+            return true;
+        }
+        if (left != null && right == null) {
+            return false;
+        }
+        if (left == null && right != null) {
+            return false;
+        }
+
+        if (left.val == right.val) {
+            return compare(left.left, right.right) && compare(left.right, right.left);
+        }
+
+        return false;
+    }
+
+    /**
+     * 解法2：DFS，迭代
+     */
+    public boolean isSymmetric3(TreeNode root) {
+        if (root == null) {
+            return false;
+        }
+
+        if (!equal(root.left, root.right)) {
+            return false;
+        }
+
+        Deque<TreeNode> st = new LinkedList<>();
+
+        st.push(root.right);
+        st.push(root.left);
+
+        TreeNode curR = root.right;
+        TreeNode curL = root.left;
+
+        while (!st.isEmpty()) {
+            curL = st.pop();
+            curR = st.pop();
+
+            // 前序，处理
+            if (!equal(curL, curR)) {
+                return false;
+            }
+
+            if (curR != null && curL != null) {
+                st.push(curL.right);
+                st.push(curR.left);
+                st.push(curR.right);
+                st.push(curL.left);
+            }
+        }
+
+        return true;
+    }
+
+    private boolean equal(TreeNode l, TreeNode r) {
+        if (l == null && r == null) {
+            return true;
+        }
+        if (l != null && r == null) {
+            return false;
+        }
+        if (l == null && r != null) {
+            return false;
+        }
+        if (l.val == r.val) {
+            return true;
+        }
+        return false;
+    }
+}
+```
 
 Python：
 
@@ -283,4 +370,4 @@ const check = (leftPtr, rightPtr) => {
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
\ No newline at end of file
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>