左程云基础班——二叉树

1. 遍历二叉树

二叉树结点：

public class Node {public int value;public Node left;public Node right;public Node(int value) {this.value = value;}
}

1）前序遍历

 public static void preOrderRecur(Node head) {if (head == null) {return;}System.out.print(head.value + " ");preOrderRecur(head.left);preOrderRecur(head.right);}public static void preOrderUnRecur(Node head) {if (head != null) {//入栈顺序根右左Stack<Node> stack = new Stack<>();stack.push(head);while (!stack.isEmpty()) {head = stack.pop();System.out.print(head.value + " ");if (head.right != null) {stack.push(head.right);}if (head.left != null) {stack.push(head.left);}}}}

2）后序遍历

 public static void postOrderRecur(Node head) {if (head == null) {return;}postOrderRecur(head.left);postOrderRecur(head.right);System.out.print(head.value + " ");}//入栈顺序根左右，逆序输出public static void postOrderUnRrecur(Node head) {if (head != null) {Stack<Node> stack = new Stack<>();Stack<Node> res = new Stack<>();stack.push(head);while (!stack.isEmpty()) {head = stack.pop();res.push(head);if (head.left != null) {stack.push(head.left);}if (head.right != null) {stack.push(head.right);}}while (!res.isEmpty()) {System.out.print(res.pop().value + " ");}}}

3）中序遍历

 public static void inOrderRecur(Node head) {if (head == null) {return;}inOrderRecur(head.left);System.out.print(head.value + " ");inOrderRecur(head.right);}//左子树全部入栈public static void inOrderUnRecur(Node head) {if (head != null) {Stack<Node> stack = new Stack<>();while (!stack.isEmpty() || head != null) {if (head != null) {stack.push(head);head = head.left;} else {head = stack.pop();System.out.print(head.value + " ");head = head.right;}}}}

4）宽度遍历（最大宽度）

public static int WildTravel(Node head) {if (head != null) {LinkedList<Node> queue = new LinkedList<>();HashMap hashMap = new HashMap<Node, Integer>();hashMap.put(head, 1);int curlevel = 0;int levelNodes = 0;int maxNodes = 0;queue.add(head);while (!queue.isEmpty()) {head = queue.poll();//                System.out.print(head.value + " ");if ((int)hashMap.get(head) > curlevel) {curlevel = (int)hashMap.get(head);levelNodes = 1;}else {levelNodes++;}maxNodes = Math.max(maxNodes, levelNodes);if (head.left != null) {hashMap.put(head.left, (int)hashMap.get(head) + 1);queue.add(head.left);}if (head.right != null) {hashMap.put(head.right, (int)hashMap.get(head) + 1);queue.add(head.right);}}return maxNodes;}return 0;}

2. 判断树结构

树形DP的套路方法：

根据左树的信息和右树的信息得到自己的信息

1）判断二叉查找树

递归实现：

    public static int preValue = Integer.MIN_VALUE;public static boolean checkBST1(Node head) {if (head == null) {return true;}boolean left = checkBST1(head.left);if (left != true) {return false;}if (head.value < preValue) {return false;}else {preValue = head.value;}return checkBST1(head.right);}

非递归实现：

 public static boolean checkBST2(Node head) {if (head != null) {int preValue = Integer.MIN_VALUE;Stack<Node> stack = new Stack<>();while (!stack.isEmpty() || head != null) {if (head != null) {stack.push(head);head = head.left;} else {head = stack.pop();if (head.value < preValue) {return false;}else {preValue = head.value;}head = head.right;}}}return true;}

套路实现：

 public static boolean checkBST3(Node head) {bData avData = chBST(head);return avData.isBST;}private static class bData {//每个结点返回三个信息public boolean isBST;public int max;public int min;public bData(boolean isBST, int max, int min) {this.isBST = isBST;this.max = max;this.min = min;}}public static bData chBST(Node head) {//边界信息不好确定，返回空//确定自己信息时再具体判断if (head == null) {return null;}bData left = chBST(head.left);bData right = chBST(head.right);int min = head.value;int max = head.value;if (left != null) {min = Math.min(min, left.min);max = Math.max(max, left.max);}if (right != null) {min = Math.min(min, right.min);max = Math.max(max, right.max);}boolean isBST = true;if (left != null && (!left.isBST || left.min > head.value)) {isBST = false;}if (right != null && (!right.isBST || right.max < head.value)) {isBST = false;}return new bData(isBST, max, min);}

2）. 判断完全二叉树

public static boolean checkCBT(Node head) {if (head != null) {boolean leaf = false;//表示以后的结点都是叶结点LinkedList<Node> queue = new LinkedList<>();queue.add(head);//基于宽度遍历while (!queue.isEmpty()) {head = queue.poll();if ((head.left == null && head.right != null)|| (leaf == true && (head.left != null || head.right != null))) {return false;}if (head.left != null) {queue.add(head.left);}if (head.right != null) {queue.add(head.right);}//此结点右树为空，以后都是叶结点else {leaf = true;}}}return true;}

3）. 判断满二叉树

 public static boolean checkFBT(Node head) {fData c = prosses(head);if (c.nodes == (1 << c.height) - 1)return true;elsereturn false;}private  static class fData{public int height;public int nodes;public fData(int height, int nodes) {this.height = height;this.nodes = nodes;}}public static fData prosses(Node head) {//套路解法if (head == null) {return new fData(0,0);}fData leftData = prosses(head.left);fData rightData = prosses(head.right);int height = Math.max(leftData.height, rightData.height) + 1;int nodes = leftData.nodes + rightData.nodes + 1;return new fData(height, nodes);}

3. 练习题

1）. 寻找最近的公共父节点

 public static Node seekRoot(Node head, Node o1, Node o2) {HashMap<Node, Node> root = new HashMap<>();root.put(head, head);storeRoot(head, root);HashSet<Node> set = new HashSet<>();Node cur = o1;while (cur != head) {set.add(cur);cur = root.get(cur);}cur = o2;while (cur != head) {if (set.contains(cur)) {return cur;}cur = root.get(cur);}return head;}public static void storeRoot(Node head, HashMap<Node, Node> root) {if (head == null) {return;}root.put(head.left, head);root.put(head.right, head);storeRoot(head.left, root);storeRoot(head.right, root);}

2）. 微软折纸面试题

 //无实体树结构的树形遍历public static void paperFolding(int N) {printPaper(1, N, true);}//i是迭代条件， N是边界， f标志左右子树private static void printPaper(int i, int N, boolean f) {if (i > N) {return;}printPaper(i + 1, N, true);String s = f == true ? "凹" : "凸";System.out.print(s + " ");printPaper(i + 1, N, false);}

3）. 序列化与反序列化（左神代码）

看懵了

 public static String serializeBT(Node head) {//边界信息if (head == null) {return "#_";}String res = head.value + "_";res += serializeBT(head.left);res += serializeBT(head.right);return res;}   //反序列化二叉树public static Node deserializeBT(String res) {LinkedList<String> strings = stringsToQueue(res);Node node = deserialzeProcess(strings);return node;}private static LinkedList<String> stringsToQueue(String s) {String[] strs = s.split("_");LinkedList<String> queue = new LinkedList<>();for (String s1 : strs) {queue.add(s1);}return queue;}private static Node deserialzeProcess(LinkedList<String> queue) {String value = queue.poll();if (value.equals("#")) {return null;}Node node = new Node(Integer.valueOf(value));node.left = deserialzeProcess(queue);node.right = deserialzeProcess(queue);return node;}

左程云基础班——二叉树相关推荐

一周刷爆LeetCode，算法da神左神（左程云）耗时100天打造算法与数据结构基础到高级全家桶教程，直击BTAJ等一线大厂必问算法面试题真题详解笔记
一周刷爆LeetCode,算法大神左神(左程云)耗时100天打造算法与数据结构基础到高级全家桶教程,直击BTAJ等一线大厂必问算法面试题真题详解笔记教程与代码地址 P1 出圈了!讲课之外我们来聊聊 ...
左程云算法笔记总结-基础篇
基础01(复杂度.基本排序) 认识复杂度和简单排序算法时间复杂度 big O 即 O(f(n)) 常数操作的数量写出来,不要低阶项,只要最高项,并且不要最高项的系数一个操作如果和样本的数据量没有关 ...
数据结构与算法XS班-左程云第八节课笔记（归并排序和快速排序）
第8节归并排序和快速排序 ##这是数据结构与算法新手班-左程云第八节课的笔记## 归并排序归并排序实际上是一个很经典的排序方法,时间复杂度o(N*logN). 递归版本(图解排序算法(四)之归并排 ...
数据结构与算法XS班-左程云第一节课笔记（位运算、算法是什么、简单排序）
第1节位运算.算法是什么.简单排序 ##这是数据结构与算法新手班-左程云第一节课的笔记## 1. 位运算 // 你们会不会表示一个数字的32位啊? // Java中int类型默认以32位二进制数在计 ...
CSDN专访左程云,算法之道
算法的庞大让很多人畏惧,程序员如何正确的学习并应用于面试.工作中呢?今天,CSDN邀请了IBM软件工程师.百度软件工程师.刷题5年的算法热爱者左程云,来担任CSDN社区问答栏目的第二十六期嘉宾,届时会 ...
一看“左程云：200道算法与数据结构”，二刷“阿里云：70+算法题、30种大厂笔试高频知识点”，3月过去终于挺进我梦中的字节！
不管是学生还是已经工作的人,我想彼此都有一个相同的梦想:进大厂! 眼看着2020年还有个三十来天就要完美收尾了,那么如何才能在未来三个月弯道超车赶上"金三银四的春招",进入梦寐以求 ...
左程云：程序员该如何学习算法？
大家好,我是左程云.我本科就读于华中科技大学.硕士毕业于在芝加哥大学.先后在IBM.百度.GrowingIO和亚马逊工作,是一个刷题7年的算法爱好者. 我是<程序员代码面试指南--IT名企算法与 ...
左程云算法笔记（四）哈希表和有序表的使用、链表
左程云算法笔记(四) 哈希表的使用有序表的使用链表单链表反转 (LC206) 双向链表反转打印两个有序链表的公共部分合并两个有序链表(LC21) 判断一个链表是否为回文结构 (LC234) ...
LeetCode左程云算法课笔记
左程云算法课笔记剑指Offer 位运算 ^运算符理解寻找出现双中的单数取出一个数最右边1的位置找所有双出现中的两个单数整数二进制奇数位偶数位交换数组中全部出现k次返回出现一次的数链表判 ...

左程云基础班——二叉树

左程云基础班——二叉树

1. 遍历二叉树

二叉树结点：

1）前序遍历

2）后序遍历

3）中序遍历

4）宽度遍历（最大宽度）

2. 判断树结构

树形DP的套路方法：

1）判断二叉查找树

递归实现：

非递归实现：

套路实现：

2）. 判断完全二叉树

3）. 判断满二叉树

3. 练习题

1）. 寻找最近的公共父节点

2）. 微软折纸面试题

3）. 序列化与反序列化（左神代码）

左程云基础班——二叉树相关推荐

最新文章

热门文章