Java版本和C++版本的二叉树序列化与反序列化
1、什么是二叉树的序列化与反序列化
二叉树就是节点在内存区域中串联起来的，但是如果掉电，内存上的数据就没有了。为了保存这种结构，将二叉树用字符串的形式保存到硬盘中，这就是序列化；从字符串形式转换为二叉树，这就是反序列化。
唯一的字符串会对应唯一的结构，唯一的结构也会对应唯一的字符串，即字符串和二叉树是一一对应的。
【思路】首先认为 NULL 是不可忽略的，遇到 NULL 就用 # 或者其他字符代替。且每访问结束一个节点，用分隔符隔开。
2、先序方式序列化和反序列化
【例子】
上图红色数字就是先序遍历的顺序，所以得到的字符串就是 “1，1，#，1，#，#，#”。
之所以要用分隔符隔开，是为了防止二义性，比如如下两棵树：
【代码实现】
//先序序列化二叉树
void preS(Treenode *root, queue<string> &ans) {
if (root == nullptr)
ans.push("#");
else {
//每个节点转成的字符串保存到队列中
ans.push(to_string(root->value));
preS(root->lchild, ans);
preS(root->rchild, ans);
}
}
queue<string> preOrderSerial(TreeNode *root) {
queue<string> ans;
preS(root, ans);
return ans;
}
TreeNode *preb(queue<string> &prelist) {
string value = prelist.front();
prelist.pop();
//空树
if (value == "#") return nullptr;
TreeNode *root = new TreeNode(stoi(value)); //每个节点字符串转成整数
root->lchild = preb(prelist);
root->rchild = preb(prelist);
return root;
}
//以先序序列化还原二叉树, 即反序列化
TreeNode *buildByPreQueue(queue<string> &prelist) {
if (prelist.size() == 0) return nullptr;
return preb(prelist);
}3、后序方式序列化和反序列化
//后序序列化
void posS(TreeNode *root, queue<string> &ans) {
if (root == nullptr)
ans.push("#");
else {
posS(root->lchild, ans);
posS(root->rchild, ans);
ans.push(to_string(root->value));
}
}
queue<string> posOrderSerial(TreeNode *root) {
queue<string> ans;
posS(root, ans);
return ans;
}
//后序反序列化
TreeNode *posB(stack<string> &posstack) {
string value = posstack.top();
posstack.pop();
if (value == "#") return nullptr;
TreeNode *root = new TreeNode(stoi(value));
root->rchild = posB(posstack);
root->lchild = posB(posstack);
return root;
}
TreeNode *buildByPosQueue(queue<string> &poslist) {
if (poslist.size() == 0)
return nullptr;
stack<string> sta; //栈中的顺序为：中右左
while (!poslist.empty()) {
sta.push(poslist.front());
poslist.pop();
}
return posB(sta);
}4、层序方式序列化和反序列化
//层序序列化
queue<string> levelSerial(TreeNode *root) {
queue<string> ans;
if (root == nullptr) {
ans.push("#");
} else {
ans.push(to_string(root->value));
//准备队列，用于层序遍历
queue<TreeNode *> que;
que.push(root);
while (!que.empty()) {
TreeNode *cur = que.front();
que.pop();
if (cur->lchild != nullptr) {
ans.push(to_string(cur->lchild->value));
que.push(cur->lchild);
} else {
ans.push("#");
}
if (cur->rchild != nullptr) {
ans.push(to_string(cur->rchild->value));
que.push(cur->rchild);
} else {
ans.push("#");
}
}
}
return ans;
}
//层序反序列化
TreeNode *generateTreeNode(string str) {
if (str == "#") return nullptr;
return new TreeNode(stoi(str));
}
TreeNode *buildByLevelQueue(queue<string> &levelList) {
if (levelList.size() == 0) {
return nullptr;
}
TreeNode *root = generateTreeNode(levelList.front());
levelList.pop();
queue<TreeNode *> que;
if (root != nullptr) {
que.push(root);
}
TreeNode *cur = nullptr;
while (!que.empty()) {
cur = que.front();
que.pop();
cur->lchild = generateTreeNode(levelList.front());
levelList.pop();
cur->rchild = generateTreeNode(levelList.front());
levelList.pop();
if (cur->lchild != nullptr) {
que.push(cur->lchild);
}
if (cur->rchild != nullptr) {
que.push(cur->rchild);
}
}
return root;
}5、完整代码 C++ 版
#include <iOStream>
#include <cstring>
#include <queue>
#include <ctime>
#include <stack>
using namespace std;
class TreeNode {
public:
int value;
TreeNode *lchild;
TreeNode *rchild;
TreeNode(int data) : value(data) {}
};
//先序序列化二叉树
void preS(TreeNode *root, queue<string> &ans) {
if (root == nullptr)
ans.push("#");
else {
//每个节点转成的字符串保存到队列中
ans.push(to_string(root->value));
preS(root->lchild, ans);
preS(root->rchild, ans);
}
}
queue<string> preOrderSerial(TreeNode *root) {
queue<string> ans;
preS(root, ans);
return ans;
}
//以先序序列化还原二叉树, 即反序列化
TreeNode *preb(queue<string> &prelist) {
string value = prelist.front();
prelist.pop();
//空树
if (value == "#") return nullptr;
TreeNode *root = new TreeNode(stoi(value)); //每个节点字符串转成整数
root->lchild = preb(prelist);
root->rchild = preb(prelist);
return root;
}
TreeNode *buildByPreQueue(queue<string> &prelist) {
if (prelist.size() == 0) return nullptr;
return preb(prelist);
}
//后序序列化
void posS(TreeNode *root, queue<string> &ans) {
if (root == nullptr)
ans.push("#");
else {
posS(root->lchild, ans);
posS(root->rchild, ans);
ans.push(to_string(root->value));
}
}
queue<string> posOrderSerial(TreeNode *root) {
queue<string> ans;
posS(root, ans);
return ans;
}
//后序反序列化
TreeNode *posB(stack<string> &posstack) {
string value = posstack.top();
posstack.pop();
if (value == "#") return nullptr;
TreeNode *root = new TreeNode(stoi(value));
root->rchild = posB(posstack);
root->lchild = posB(posstack);
return root;
}
TreeNode *buildByPosQueue(queue<string> &poslist) {
if (poslist.size() == 0)
return nullptr;
stack<string> sta; //栈中的顺序为：中右左
while (!poslist.empty()) {
sta.push(poslist.front());
poslist.pop();
}
return posB(sta);
}
//层序序列化
queue<string> levelSerial(TreeNode *root) {
queue<string> ans;
if (root == nullptr) {
ans.push("#");
} else {
ans.push(to_string(root->value));
//准备队列，用于层序遍历
queue<TreeNode *> que;
que.push(root);
while (!que.empty()) {
TreeNode *cur = que.front();
que.pop();
if (cur->lchild != nullptr) {
ans.push(to_string(cur->lchild->value));
que.push(cur->lchild);
} else {
ans.push("#");
}
if (cur->rchild != nullptr) {
ans.push(to_string(cur->rchild->value));
que.push(cur->rchild);
} else {
ans.push("#");
}
}
}
return ans;
}
//层序反序列化
TreeNode *generateTreeNode(string str) {
if (str == "#") return nullptr;
return new TreeNode(stoi(str));
}
TreeNode *buildByLevelQueue(queue<string> &levelList) {
if (levelList.size() == 0) {
return nullptr;
}
TreeNode *root = generateTreeNode(levelList.front());
levelList.pop();
queue<TreeNode *> que;
if (root != nullptr) {
que.push(root);
}
TreeNode *cur = nullptr;
while (!que.empty()) {
cur = que.front();
que.pop();
cur->lchild = generateTreeNode(levelList.front());
levelList.pop();
cur->rchild = generateTreeNode(levelList.front());
levelList.pop();
if (cur->lchild != nullptr) {
que.push(cur->lchild);
}
if (cur->rchild != nullptr) {
que.push(cur->rchild);
}
}
return root;
}
//for test
TreeNode *generate(int level, int maxLevel, int maxValue) {
if (level > maxLevel || rand() % 100 < 0.5) return nullptr;
TreeNode *root = new TreeNode(rand() % maxValue);
root->lchild = generate(level + 1, maxLevel, maxValue);
root->rchild = generate(level + 1, maxLevel, maxValue);
return root;
}
TreeNode *generateRandomBST(int maxLen, int maxVal) {
return generate(1, maxLen, maxVal);
}
bool isSameValueStructure(TreeNode *root1, TreeNode *root2) {
if (root1 == nullptr && root2 != nullptr)
return false;
if (root1 != nullptr && root2 == nullptr)
return false;
if (root1 == nullptr && root2 == nullptr)
return true;
if (root1->value != root2->value)
return false;
return isSameValueStructure(root1->lchild, root2->lchild) && isSameValueStructure(root1->rchild, root2->rchild);
}
string getSpace(int num) {
string space = "";
for (int i = 0; i < num; i++) {
space += " ";
}
return space;
}
void printInOrder(TreeNode *root, int height, string to, int len) {
if (root == nullptr) return ;
printInOrder(root->rchild, height + 1, "v", len);
string val = to + to_string(root->value) + to;
int lenM = val.length();
int lenL = (len - lenM) / 2;
int lenR = len - lenM - lenL;
val = getSpace(lenL) + val + getSpace(lenR);
cout << getSpace(height * len) + val << endl;
printInOrder(root->lchild, height + 1, "^", len);
}
void printTree(TreeNode *root) {
cout << "Binary Tree:" << endl;
printInOrder(root, 0, "H", 7);
cout << endl;
}
int main() {
srand(time(0));
int maxLevel = 5;
int maxValue = 100;
int testTime = 1000000;
cout << "test begin" << endl;
for (int i = 0; i < testTime + 1; i++) {
TreeNode *root = generateRandomBST(maxLevel, maxValue);
queue<string> pre = preOrderSerial(root);
queue<string> post = posOrderSerial(root);
queue<string> level = levelSerial(root);
TreeNode *preBuild = buildByPreQueue(pre);
TreeNode *posBuild = buildByPosQueue(post);
TreeNode *levelBuild = buildByLevelQueue(level);
if (!isSameValueStructure(preBuild, posBuild) || !isSameValueStructure(posBuild, levelBuild)) {
cout << "Oops!" << endl;
break;
}
if (i && i % 100 == 0) cout << i << " cases passed!" << endl;
}
cout << "test finish!" << endl;
return 0;
}Java 版
package class11;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
public class Code02_SerializeAndReconstructTree {
public static class Node {
public int value;
public Node left;
public Node right;
public Node(int data) {
this.value = data;
}
}
public static Queue<String> preSerial(Node head) {
Queue<String> ans = new LinkedList<>();
pres(head, ans);
return ans;
}
public static void pres(Node head, Queue<String> ans) {
if (head == null) {
ans.add(null);
} else {
ans.add(String.valueOf(head.value));
pres(head.left, ans);
pres(head.right, ans);
}
}
public static Queue<String> inSerial(Node head) {
Queue<String> ans = new LinkedList<>();
ins(head, ans);
return ans;
}
public static void ins(Node head, Queue<String> ans) {
if (head == null) {
ans.add(null);
} else {
ins(head.left, ans);
ans.add(String.valueOf(head.value));
ins(head.right, ans);
}
}
public static Queue<String> posSerial(Node head) {
Queue<String> ans = new LinkedList<>();
poss(head, ans);
return ans;
}
public static void poss(Node head, Queue<String> ans) {
if (head == null) {
ans.add(null);
} else {
poss(head.left, ans);
poss(head.right, ans);
ans.add(String.valueOf(head.value));
}
}
public static Node buildByPreQueue(Queue<String> prelist) {
if (prelist == null || prelist.size() == 0) {
return null;
}
return preb(prelist);
}
public static Node preb(Queue<String> prelist) {
String value = prelist.poll();
if (value == null) {
return null;
}
Node head = new Node(Integer.valueOf(value));
head.left = preb(prelist);
head.right = preb(prelist);
return head;
}
public static Node buildByPosQueue(Queue<String> poslist) {
if (poslist == null || poslist.size() == 0) {
return null;
}
// 左右中 -> stack(中右左)
Stack<String> stack = new Stack<>();
while (!poslist.isEmpty()) {
stack.push(poslist.poll());
}
return posb(stack);
}
public static Node posb(Stack<String> posstack) {
String value = posstack.pop();
if (value == null) {
return null;
}
Node head = new Node(Integer.valueOf(value));
head.right = posb(posstack);
head.left = posb(posstack);
return head;
}
public static Queue<String> levelSerial(Node head) {
Queue<String> ans = new LinkedList<>();
if (head == null) {
ans.add(null);
} else {
ans.add(String.valueOf(head.value));
Queue<Node> queue = new LinkedList<Node>();
queue.add(head);
while (!queue.isEmpty()) {
head = queue.poll(); // head 父 子
if (head.left != null) {
ans.add(String.valueOf(head.left.value));
queue.add(head.left);
} else {
ans.add(null);
}
if (head.right != null) {
ans.add(String.valueOf(head.right.value));
queue.add(head.right);
} else {
ans.add(null);
}
}
}
return ans;
}
public static Node buildByLevelQueue(Queue<String> levelList) {
if (levelList == null || levelList.size() == 0) {
return null;
}
Node head = generateNode(levelList.poll());
Queue<Node> queue = new LinkedList<Node>();
if (head != null) {
queue.add(head);
}
Node node = null;
while (!queue.isEmpty()) {
node = queue.poll();
node.left = generateNode(levelList.poll());
node.right = generateNode(levelList.poll());
if (node.left != null) {
queue.add(node.left);
}
if (node.right != null) {
queue.add(node.right);
}
}
return head;
}
public static Node generateNode(String val) {
if (val == null) {
return null;
}
return new Node(Integer.valueOf(val));
}
// for test
public static Node generateRandomBST(int maxLevel, int maxValue) {
return generate(1, maxLevel, maxValue);
}
// for test
public static Node generate(int level, int maxLevel, int maxValue) {
if (level > maxLevel || Math.random() < 0.5) {
return null;
}
Node head = new Node((int) (Math.random() * maxValue));
head.left = generate(level + 1, maxLevel, maxValue);
head.right = generate(level + 1, maxLevel, maxValue);
return head;
}
// for test
public static boolean isSameValueStructure(Node head1, Node head2) {
if (head1 == null && head2 != null) {
return false;
}
if (head1 != null && head2 == null) {
return false;
}
if (head1 == null && head2 == null) {
return true;
}
if (head1.value != head2.value) {
return false;
}
return isSameValueStructure(head1.left, head2.left) && isSameValueStructure(head1.right, head2.right);
}
// for test
public static void printTree(Node head) {
System.out.println("Binary Tree:");
printInOrder(head, 0, "H", 17);
System.out.println();
}
public static void printInOrder(Node head, int height, String to, int len) {
if (head == null) {
return;
}
printInOrder(head.right, height + 1, "v", len);
String val = to + head.value + to;
int lenM = val.length();
int lenL = (len - lenM) / 2;
int lenR = len - lenM - lenL;
val = getSpace(lenL) + val + getSpace(lenR);
System.out.println(getSpace(height * len) + val);
printInOrder(head.left, height + 1, "^", len);
}
public static String getSpace(int num) {
String space = " ";
StringBuffer buf = new StringBuffer("");
for (int i = 0; i < num; i++) {
buf.append(space);
}
return buf.toString();
}
public static void main(String[] args) {
int maxLevel = 5;
int maxValue = 100;
int testTimes = 1000000;
System.out.println("test begin");
for (int i = 0; i < testTimes; i++) {
Node head = generateRandomBST(maxLevel, maxValue);
Queue<String> pre = preSerial(head);
Queue<String> pos = posSerial(head);
Queue<String> level = levelSerial(head);
Node preBuild = buildByPreQueue(pre);
Node posBuild = buildByPosQueue(pos);
Node levelBuild = buildByLevelQueue(level);
if (!isSameValueStructure(preBuild, posBuild) || !isSameValueStructure(posBuild, levelBuild)) {
System.out.println("Oops!");
}
}
System.out.println("test finish!");
}
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