From cf77fa5d9be30d5d6f5d4e91baa6f01d68d4f516 Mon Sep 17 00:00:00 2001 From: markilue <745518019@qq.com> Date: Sun, 8 Jan 2023 13:02:04 +0800 Subject: [PATCH] =?UTF-8?q?leecode=E6=9B=B4=E6=96=B0?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../{InvertTree.java => T05_InvertTree.java} | 2 +- ...{IsSymmetric.java => T06_IsSymmetric.java} | 2 +- ...rsal.java => T01_0_PreOrderTraversal.java} | 2 +- .../leecode/tree/second/T01_1_Preorder.java | 71 +++++++++++ ...sal.java => T02_0_PostOrderTraversal.java} | 2 +- .../leecode/tree/second/T02_1_Postorder.java | 76 ++++++++++++ ..._LevelOrder.java => T04_0_LevelOrder.java} | 2 +- ...ottom.java => T04_1_LevelOrderBottom.java} | 2 +- ...SideView.java => T04_2_RightSideView.java} | 2 +- ...Levels.java => T04_3_averageOfLevels.java} | 2 +- ..._LevelOrder.java => T04_4_LevelOrder.java} | 2 +- ...stValues.java => T04_5_LargestValues.java} | 2 +- .../{T046_Connect.java => T04_6_Connect.java} | 2 +- .../{T047_Connect.java => T04_7_Connect.java} | 2 +- ...T048_MaxDepth.java => T04_8_MaxDepth.java} | 2 +- ...T049_MinDepth.java => T04_9_MinDepth.java} | 2 +- .../leecode/tree/second/T05_InvertTree.java | 67 ++++++++++ .../leecode/tree/second/T06_IsSymmetric.java | 114 ++++++++++++++++++ 18 files changed, 342 insertions(+), 14 deletions(-) rename Leecode/src/main/java/com/markilue/leecode/tree/{InvertTree.java => T05_InvertTree.java} (99%) rename Leecode/src/main/java/com/markilue/leecode/tree/{IsSymmetric.java => T06_IsSymmetric.java} (99%) rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T01_PreOrderTraversal.java => T01_0_PreOrderTraversal.java} (99%) create mode 100644 Leecode/src/main/java/com/markilue/leecode/tree/second/T01_1_Preorder.java rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T02_PostOrderTraversal.java => T02_0_PostOrderTraversal.java} (99%) create mode 100644 Leecode/src/main/java/com/markilue/leecode/tree/second/T02_1_Postorder.java rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T04_LevelOrder.java => T04_0_LevelOrder.java} (98%) rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T041_LevelOrderBottom.java => T04_1_LevelOrderBottom.java} (98%) rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T042_RightSideView.java => T04_2_RightSideView.java} (98%) rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T043_averageOfLevels.java => T04_3_averageOfLevels.java} (99%) rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T044_LevelOrder.java => T04_4_LevelOrder.java} (98%) rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T045_LargestValues.java => T04_5_LargestValues.java} (98%) rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T046_Connect.java => T04_6_Connect.java} (98%) rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T047_Connect.java => T04_7_Connect.java} (99%) rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T048_MaxDepth.java => T04_8_MaxDepth.java} (98%) rename Leecode/src/main/java/com/markilue/leecode/tree/second/{T049_MinDepth.java => T04_9_MinDepth.java} (99%) create mode 100644 Leecode/src/main/java/com/markilue/leecode/tree/second/T05_InvertTree.java create mode 100644 Leecode/src/main/java/com/markilue/leecode/tree/second/T06_IsSymmetric.java diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/InvertTree.java b/Leecode/src/main/java/com/markilue/leecode/tree/T05_InvertTree.java similarity index 99% rename from Leecode/src/main/java/com/markilue/leecode/tree/InvertTree.java rename to Leecode/src/main/java/com/markilue/leecode/tree/T05_InvertTree.java index 768ae4e..faa9991 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/InvertTree.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/T05_InvertTree.java @@ -16,7 +16,7 @@ import java.util.Queue; * @Version: 1.0 */ -public class InvertTree { +public class T05_InvertTree { @Test diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/IsSymmetric.java b/Leecode/src/main/java/com/markilue/leecode/tree/T06_IsSymmetric.java similarity index 99% rename from Leecode/src/main/java/com/markilue/leecode/tree/IsSymmetric.java rename to Leecode/src/main/java/com/markilue/leecode/tree/T06_IsSymmetric.java index 6dd2993..5327bde 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/IsSymmetric.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/T06_IsSymmetric.java @@ -16,7 +16,7 @@ import java.util.Queue; * 给你一个二叉树的根节点 root ， 检查它是否轴对称。 * @Version: 1.0 */ -public class IsSymmetric { +public class T06_IsSymmetric { @Test public void test() { diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T01_PreOrderTraversal.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T01_0_PreOrderTraversal.java similarity index 99% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T01_PreOrderTraversal.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T01_0_PreOrderTraversal.java index f6f24f8..c612464 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T01_PreOrderTraversal.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T01_0_PreOrderTraversal.java @@ -16,7 +16,7 @@ import java.util.*; * 给你二叉树的根节点 root ，返回它节点值的 前序 遍历。 *@Version: 1.0 */ -public class T01_PreOrderTraversal { +public class T01_0_PreOrderTraversal { @Test public void test() { diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T01_1_Preorder.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T01_1_Preorder.java new file mode 100644 index 0000000..5852e4a --- /dev/null +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T01_1_Preorder.java @@ -0,0 +1,71 @@ +package com.markilue.leecode.tree.second; + +import java.util.ArrayList; +import java.util.List; +import java.util.Stack; + +/** + *@BelongsProject: Leecode + *@BelongsPackage: com.markilue.leecode.tree.second + *@Author: dingjiawen + *@CreateTime: 2023-01-08 11:36 + *@Description: + * TODO 力扣589题 N叉树的前序遍历: + * 给定一个 n 叉树的根节点 root ，返回 其节点值的 前序遍历 。 + * n 叉树 在输入中按层序遍历进行序列化表示，每组子节点由空值 null 分隔（请参见示例）。 + *@Version: 1.0 + */ +public class T01_1_Preorder { + + /** + * 思路:与前序遍历一致,只是从遍历left和right变成了children，迭代法 + * 速度击败17.14%，内存击败39.29% + * @param root + * @return + */ + public List preorder(NNode root) { + List result = new ArrayList<>(); + if(root==null){ + return result; + } + + Stack stack = new Stack<>(); + stack.push(root); + while (!stack.isEmpty()){ + NNode node = stack.pop(); + result.add(node.val); + for (int i = node.children.size()-1; i >=0 ; i--) { + NNode child = node.children.get(i); + if(child!=null){ + stack.push(child); + } + } + } + return result; + + } + + + /** + * 思路:递归法 + * 速度击败100%，内存击败17.14% + * @param root + * @return + */ + List result = new ArrayList<>(); + public List preorder1(NNode root) { + travel(root); + return result; + + } + + public void travel(NNode root) { + if(root==null){ + return; + } + result.add(root.val); + for (NNode child : root.children) { + travel(child); + } + } +} diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T02_PostOrderTraversal.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T02_0_PostOrderTraversal.java similarity index 99% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T02_PostOrderTraversal.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T02_0_PostOrderTraversal.java index 984cb52..a254d11 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T02_PostOrderTraversal.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T02_0_PostOrderTraversal.java @@ -16,7 +16,7 @@ import java.util.*; * 给你一棵二叉树的根节点 root ，返回其节点值的 后序遍历 。 *@Version: 1.0 */ -public class T02_PostOrderTraversal { +public class T02_0_PostOrderTraversal { @Test public void test() { diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T02_1_Postorder.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T02_1_Postorder.java new file mode 100644 index 0000000..5a4182b --- /dev/null +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T02_1_Postorder.java @@ -0,0 +1,76 @@ +package com.markilue.leecode.tree.second; + +import com.markilue.leecode.tree.TreeNode; +import com.markilue.leecode.tree.TreeUtils; +import org.junit.Test; + +import java.util.*; + +/** + *@BelongsProject: Leecode + *@BelongsPackage: com.markilue.leecode.tree.second + *@Author: dingjiawen + *@CreateTime: 2023-01-05 10:25 + *@Description: + * TODO 二刷leecode145题 二叉树的后序遍历: + * 给你一棵二叉树的根节点 root ，返回其节点值的 后序遍历 。 + *@Version: 1.0 + */ +public class T02_1_Postorder { + + + /** + * 思路:递归法 + * 速度击败100%，内存击败49.35% + * @param root + * @return + */ + List result; + public List postorderTraversal(NNode root) { + result=new ArrayList<>(); + postTraversal(root); + return result; + + } + public void postTraversal(NNode root) { + if(root==null){ + return; + } + for (NNode child : root.children) { + postTraversal(child); + } + result.add(root.val); + + } + + + /** + * 思路:stack迭代法:中后前——>反序前后中 + * 速度击败26.37% 内存击败50.42% + * @param root + * @return + */ + public List postorderTraversal1(NNode root) { + List result = new ArrayList<>(); + if(root==null){ + return result; + } + Stack stack = new Stack<>(); + stack.push(root); + while (!stack.isEmpty()){ + NNode node = stack.pop(); + result.add(node.val); + for (NNode child : node.children) { + stack.push(child); + } + } + Collections.reverse(result); + return result; + + + } + + + + +} diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_LevelOrder.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_0_LevelOrder.java similarity index 98% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T04_LevelOrder.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T04_0_LevelOrder.java index 2885331..74c3be7 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_LevelOrder.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_0_LevelOrder.java @@ -16,7 +16,7 @@ import java.util.*; * 给你二叉树的根节点 root ，返回其节点值的 层序遍历 。 （即逐层地，从左到右访问所有节点）。 *@Version: 1.0 */ -public class T04_LevelOrder { +public class T04_0_LevelOrder { @Test public void test() { diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T041_LevelOrderBottom.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_1_LevelOrderBottom.java similarity index 98% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T041_LevelOrderBottom.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T04_1_LevelOrderBottom.java index 586ae70..85bd410 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T041_LevelOrderBottom.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_1_LevelOrderBottom.java @@ -17,7 +17,7 @@ import java.util.*; * （即按从叶子节点所在层到根节点所在的层，逐层从左向右遍历） *@Version: 1.0 */ -public class T041_LevelOrderBottom { +public class T04_1_LevelOrderBottom { @Test public void test() { diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T042_RightSideView.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_2_RightSideView.java similarity index 98% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T042_RightSideView.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T04_2_RightSideView.java index d602304..b44c5f1 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T042_RightSideView.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_2_RightSideView.java @@ -17,7 +17,7 @@ import java.util.Queue; * 给定一个二叉树的 根节点 root，想象自己站在它的右侧，按照从顶部到底部的顺序，返回从右侧所能看到的节点值。 *@Version: 1.0 */ -public class T042_RightSideView { +public class T04_2_RightSideView { /** * 思路：就是返回他所有最右侧的节点，层序遍历确实可以解决，返回每一层最后的节点 diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T043_averageOfLevels.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_3_averageOfLevels.java similarity index 99% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T043_averageOfLevels.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T04_3_averageOfLevels.java index f1c2c9e..ad2cc01 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T043_averageOfLevels.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_3_averageOfLevels.java @@ -16,7 +16,7 @@ import java.util.*; * 给定一个非空二叉树的根节点 root , 以数组的形式返回每一层节点的平均值。与实际答案相差 10-5 以内的答案可以被接受。 *@Version: 1.0 */ -public class T043_averageOfLevels { +public class T04_3_averageOfLevels { @Test public void test() { diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T044_LevelOrder.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_4_LevelOrder.java similarity index 98% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T044_LevelOrder.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T04_4_LevelOrder.java index c506e87..450b6f4 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T044_LevelOrder.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_4_LevelOrder.java @@ -16,7 +16,7 @@ import java.util.Queue; * 树的序列化输入是用层序遍历，每组子节点都由 null 值分隔（参见示例）。 *@Version: 1.0 */ -public class T044_LevelOrder { +public class T04_4_LevelOrder { /** * 思路：N叉树的层序遍历本质上和二叉树无异BFS层序遍历版 diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T045_LargestValues.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_5_LargestValues.java similarity index 98% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T045_LargestValues.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T04_5_LargestValues.java index 6d11de1..66ed190 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T045_LargestValues.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_5_LargestValues.java @@ -17,7 +17,7 @@ import java.util.Queue; * 给定一棵二叉树的根节点 root ，请找出该二叉树中每一层的最大值。 *@Version: 1.0 */ -public class T045_LargestValues { +public class T04_5_LargestValues { /** diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T046_Connect.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_6_Connect.java similarity index 98% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T046_Connect.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T04_6_Connect.java index c60ae06..fcaf7a4 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T046_Connect.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_6_Connect.java @@ -24,7 +24,7 @@ import java.util.List; * 初始状态下，所有 next 指针都被设置为 NULL。 *@Version: 1.0 */ -public class T046_Connect { +public class T04_6_Connect { /** diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T047_Connect.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_7_Connect.java similarity index 99% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T047_Connect.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T04_7_Connect.java index e5ea8ce..bb976aa 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T047_Connect.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_7_Connect.java @@ -24,7 +24,7 @@ import java.util.List; * 与T46似乎完全一致,所以代码完全没有改动 *@Version: 1.0 */ -public class T047_Connect { +public class T04_7_Connect { /** diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T048_MaxDepth.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_8_MaxDepth.java similarity index 98% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T048_MaxDepth.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T04_8_MaxDepth.java index 173d3a5..e525dde 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T048_MaxDepth.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_8_MaxDepth.java @@ -17,7 +17,7 @@ import java.util.Queue; * 说明: 叶子节点是指没有子节点的节点。 *@Version: 1.0 */ -public class T048_MaxDepth { +public class T04_8_MaxDepth { /** * 思路:深度本质上就是要遍历到最底层 diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T049_MinDepth.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_9_MinDepth.java similarity index 99% rename from Leecode/src/main/java/com/markilue/leecode/tree/second/T049_MinDepth.java rename to Leecode/src/main/java/com/markilue/leecode/tree/second/T04_9_MinDepth.java index edeac2b..2a34655 100644 --- a/Leecode/src/main/java/com/markilue/leecode/tree/second/T049_MinDepth.java +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T04_9_MinDepth.java @@ -21,7 +21,7 @@ import java.util.Queue; * 说明：叶子节点是指没有子节点的节点。 *@Version: 1.0 */ -public class T049_MinDepth { +public class T04_9_MinDepth { @Test public void test() { diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T05_InvertTree.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T05_InvertTree.java new file mode 100644 index 0000000..60d7e79 --- /dev/null +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T05_InvertTree.java @@ -0,0 +1,67 @@ +package com.markilue.leecode.tree.second; + +import com.markilue.leecode.tree.TreeNode; + +import java.util.Stack; + +/** + *@BelongsProject: Leecode + *@BelongsPackage: com.markilue.leecode.tree.second + *@Author: dingjiawen + *@CreateTime: 2023-01-08 11:04 + *@Description: + * TODO 翻转二叉树: + * 给你一棵二叉树的根节点 root ，翻转这棵二叉树，并返回其根节点。 + *@Version: 1.0 + */ +public class T05_InvertTree { + + /** + * 思路:递归法 + * 速度击败100%，内存击败5.28% + * @param root + * @return + */ + public TreeNode invertTree(TreeNode root) { + if(root==null||(root.left==null&&root.right==null)){ + return root; + } + TreeNode temp=root.left; + root.left=invertTree(root.right); + root.right=invertTree(temp); + return root; + } + + + /** + * 思路:迭代法：前序遍历;层序遍历也可 + * 速度击败100%，内存击败5.28% + * @param root + * @return + */ + public TreeNode invertTree1(TreeNode root) { + if(root==null||(root.left==null&&root.right==null)){ + return root; + } + + Stack stack = new Stack<>(); + TreeNode cur=root; + while (cur!=null||!stack.isEmpty()){ + if(cur!=null){ + if(root.left!=null||root.right!=null){ + TreeNode temp=cur.left; + cur.left=cur.right; + cur.right=temp; + } + stack.push(cur); + cur=cur.left; + }else { + TreeNode node = stack.pop(); + cur=node.right; + } + } + return root; + + + } +} diff --git a/Leecode/src/main/java/com/markilue/leecode/tree/second/T06_IsSymmetric.java b/Leecode/src/main/java/com/markilue/leecode/tree/second/T06_IsSymmetric.java new file mode 100644 index 0000000..dc2f612 --- /dev/null +++ b/Leecode/src/main/java/com/markilue/leecode/tree/second/T06_IsSymmetric.java @@ -0,0 +1,114 @@ +package com.markilue.leecode.tree.second; + +import com.markilue.leecode.tree.TreeNode; + +import java.util.Deque; +import java.util.LinkedList; +import java.util.Queue; + +/** + *@BelongsProject: Leecode + *@BelongsPackage: com.markilue.leecode.tree.second + *@Author: dingjiawen + *@CreateTime: 2023-01-08 12:23 + *@Description: + * TODO 二刷力扣101 对称二叉树: + * 给你一个二叉树的根节点 root ， 检查它是否轴对称。 + *@Version: 1.0 + */ +public class T06_IsSymmetric { + + /** + * 递归法 + * 速度击败100%，内存击败26.75% + * @param root + * @return + */ + public boolean isSymmetric(TreeNode root) { + if (root.left == null && root.right == null) { + return true; + } else { + return find(root.left, root.right); + } + + } + + public boolean find(TreeNode node1, TreeNode node2) { + if (node1 == null && node2 == null) { + return true; + } else { + if (node1 != null && node2 != null && node1.val == node2.val) { + return find(node1.left, node2.right) && find(node1.right, node2.left); + } else { + return false; + } + + } + } + + + /** + * 迭代法：理论上来说只能层序遍历,需要频繁地队列出入栈，比较慢 + * 速度击败22.81%，内存击败59.3% + * @param root + * @return + */ + public boolean isSymmetric1(TreeNode root) { + + Deque queue = new LinkedList<>(); + queue.offer(root.left); + queue.offer(root.right); + + while (!queue.isEmpty()){ + TreeNode node1 = queue.removeFirst(); + TreeNode node2 = queue.removeLast(); + if((node1==null&&node2==null)){ + continue; + } + if(node1!=null&&node2!=null&&node1.val==node2.val){ + queue.addFirst(node1.left); + queue.addLast(node2.right); + queue.addFirst(node1.right); + queue.addLast(node2.left); + }else{ + return false; + } + } + return true; + + } + + + /** + * 官方的迭代法:事实上不需要双端队列加在头尾，只需要成对取即可 + * @param root + * @return + */ + public boolean isSymmetric2(TreeNode root) { + return check(root, root); + } + + public boolean check(TreeNode u, TreeNode v) { + Queue q = new LinkedList(); + q.offer(u); + q.offer(v); + while (!q.isEmpty()) { + u = q.poll(); + v = q.poll(); + if (u == null && v == null) { + continue; + } + if ((u == null || v == null) || (u.val != v.val)) { + return false; + } + + q.offer(u.left); + q.offer(v.right); + + q.offer(u.right); + q.offer(v.left); + } + return true; + } + +}