Binary tree serialization and deserialization (leetcode (difficult))

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Preface

One 、 Topic explanation

Topic link
1. Sequence serialization after sequence

#define _CRT_SECURE_NO_WARNINGS 1
#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<list>
#include<string>
#include<queue>
using std::cout;
using std::cin;
using std::endl;
using std::list;
using std::string;
using std::to_string;
using std::queue;
using std::pair;
struct TreeNode {
    
	int val;
	TreeNode* left;
	TreeNode* right;
	TreeNode(int x) : val(x), left(NULL), right(NULL) {
    }
};
struct Codec//,ǰ
{
    
	string str;
	void _ToString(TreeNode* root)
{
    
	if (root == nullptr)
		{
    
		str += "null,";
		return;
		}
	_ToString(root->left);
		_ToString(root->right);
	str += to_string(root->val) + ',';
	}
	string serialize(TreeNode* root) {
    
		_ToString(root);
		return str;
	}
	TreeNode* BulidTree(list<string>& h)
{
    
		if (h.back() == "null")
	{
    
		h.pop_back();//front
			return nullptr;
		}
	string f = h.back();//front
		TreeNode* root = new TreeNode(stoi(f));
	h.pop_back();
	root->right = BulidTree(h);//root->left
	root->left = BulidTree(h);//root->right
	return root;
}
TreeNode* deserialize(string data) {
    
	list<string> h = list<string>();
		string tmp = "";
	auto it = data.begin();
		while (it != data.end())
		{
    
			if (*it == ',')
			{
    
				h.push_back(tmp);
				tmp.clear();
			}
			else
			{
    
				tmp += *it;
			}
			
		 it++;
		}
		return BulidTree(h);
	}
};
struct Codec//
{
    
	string str;
	void _ToString(TreeNode* root)
	{
    
		if (root == nullptr)
		{
    
			str += "null,";
			return;
		}
		queue<TreeNode*> q;
		q.push(root);
		str += to_string(root->val)+',';
		while (!q.empty())
		{
    
			TreeNode* cur= q.front();
			q.pop();
			if (cur->left)
			{
    
				q.push(cur->left);
				str += to_string(cur->left->val) + ',';
			}
			else
			{
    
				str += "null,";
			}

			if (cur->right)
			{
    
				q.push(cur->right);
				str += to_string(cur->right->val) + ',';
			}
			else
			{
    
				str += "null,";
			}
		}
	}
	string serialize(TreeNode* root) {
    
		_ToString(root);
		return str;
	}
	TreeNode* BulidNode(string& s)
	{
    
		if (s == "null")
		{
    
			return nullptr;
		}
		return new TreeNode(stoi(s));
	}
	TreeNode* BulidTree(list<string>& h)
	{
    
		if (h.front() == "null")
		{
    
			return nullptr;
		}
		queue<TreeNode*> q;
		TreeNode* root = BulidNode(h.front());
		h.pop_front();
		q.push(root);
		while (!q.empty())
		{
    
			while (!h.empty())
			{
    
				TreeNode* cur = q.front();
				q.pop();
				if (h.front() == "null")
				{
    
					cur->left = nullptr;
					h.pop_front();
				}
				else
				{
    
					cur->left = BulidNode(h.front());
					q.push(cur->left);
					h.pop_front();
				}
				if (h.front() == "null")
				{
    
					cur->right = nullptr;
					h.pop_front();
				}
				else
				{
    
					cur->right = BulidNode(h.front());
					q.push(cur->right);
					h.pop_front();
				}

			}
		}
		return root;
	}
	TreeNode* deserialize(string data) {
    
		list<string> h = list<string>();
		string tmp = "";
		auto it = data.begin();
		while (it != data.end())
		{
    
			if (*it == ',')
			{
    
				h.push_back(tmp);
				tmp.clear();
			}
			else
			{
    
				tmp += *it;
			}

			it++;
		}
		return BulidTree(h);
	}
};
void test()
{
    
	TreeNode* node1 = new TreeNode(1);
	TreeNode* node2 = new TreeNode(2);
	TreeNode* node3 = new TreeNode(3);
	TreeNode* node4 = new TreeNode(4);
	TreeNode* node5 = new TreeNode(5);
	node1->left = node2;
	node1->right = node3;
	node3->left = node4;
	node3->right = node5;
	Codec G;
	string S = G.serialize(node1);
	Codec H;
	cout << S << endl;
	TreeNode* TR = H.deserialize(S);

}
int main()
{
    
	test();
}

summary

The key to solving the problem is to deserialize what is serialized