C++二叉树操作合集

#include <bits/stdc++.h>

using namespace std;

struct TreeNode
{
	int val;
	struct TreeNode* left;
	struct TreeNode* right;
	TreeNode(int x):val(x),left(nullptr),right(nullptr){}
};
//创建二叉树
TreeNode* createBiTree(vector<int>& TreeArray, int start)
{
	if (TreeArray.empty()) return NULL;
	if (TreeArray[start] == '#') return NULL;
	int n = TreeArray.size();
	TreeNode* root = new TreeNode(TreeArray[start]);
	int lnode = start * 2 + 1;
	int rnode = start * 2 + 2;
	if (lnode > n - 1)
	{
		root->left = NULL;
	}
	else
	{
		root->left = createBiTree(TreeArray, lnode);
	}
	if (rnode > n - 1)
	{
		root->right = NULL;
	}
	else
	{
		root->right = createBiTree(TreeArray, rnode);
	}
	return root;
}

//先中后序遍历（递归法）
void traversal(TreeNode* cur, vector<int>& vec)
{
	if (cur == NULL)
	{
		return;
	}
	//先序遍历
	vec.push_back(cur->val);
	traversal(cur->left, vec);
	traversal(cur->right, vec);

	//中序遍历
	//traversal(cur->left, vec);
	//vec.push_back(cur->val);
	//traversal(cur->right, vec);
	
	//后序遍历
	//traversal(cur->left, vec);
	//traversal(cur->right, vec);
	//vec.push_back(cur->val);
}

//先序遍历（迭代法）
vector<int> preorderTraversal(TreeNode* root)
{
	stack<TreeNode*> st;
	vector<int> result;
	if (root != NULL) st.push(root);
	while (!st.empty())
	{
		TreeNode* node = st.top();
		st.pop();
		result.push_back(node->val);
		if (node->right) st.push(node->right);
		if (node->left) st.push(node->left);
	}
	return result;
}

//层序遍历(简单写法，返回一维数组）
vector<int> levelOrder(TreeNode* root)
{
	queue<TreeNode*> que;
	if (root != NULL) que.push(root);
	vector<int> result;
	while (!que.empty())
	{
		TreeNode* node = que.front();
		que.pop();
		result.push_back(node->val);
		if (node->left) que.push(node->left);
		if (node->right) que.push(node->right);
	}
	return result;
}

//层序遍历（返回二维数组）
vector<vector<int>> levelOrder2(TreeNode* root)
{
	queue<TreeNode*> que;
	if (root != NULL) que.push(root);
	vector<vector<int>> result;
	while (!que.empty())
	{
		int size = que.size();
		vector<int> vec;
		for (int i = 0; i < size; i++)
		{
			TreeNode* node = que.front();
			que.pop();
			vec.push_back(node->val);
			if (node->left) que.push(node->left);
			if (node->right) que.push(node->right);
		}
		result.push_back(vec);
	}
	return result;
}

//翻转二叉树（递归法）
void invertTree(TreeNode* root)
{
	if (root == NULL) return;
	swap(root->left, root->right);
	invertTree(root->left);
	invertTree(root->right);
}

//翻转二叉树（迭代法，深度优先）
void invertTree2(TreeNode* root)
{
	if (root == NULL) return;
	stack<TreeNode*> st;
	st.push(root);
	while (!st.empty())
	{
		TreeNode* node = st.top();
		st.pop();
		swap(node->left, node->right);
		if (node->right) st.push(node->right);
		if (node->left) st.push(node->left);
	}
}

//翻转二叉树（迭代法，广度优先）
void invertTree3(TreeNode* root)
{
	if (root == NULL) return;
	queue<TreeNode*> que;
	que.push(root);
	while (!que.empty())
	{
		TreeNode* node = que.front();
		que.pop();
		swap(node->left, node->right);
		if (node->left) que.push(node->left);
		if (node->right) que.push(node->right);
	}
}

//合并二叉树（递归法）
TreeNode* mergeTree(TreeNode* t1, TreeNode* t2)
{
	if (t1 == NULL) return t2;
	if (t2 == NULL) return t1;
	TreeNode* root = new TreeNode(0);
	root->val = t1->val + t2->val;
	root->left = mergeTree(t1->left, t2->left);
	root->right = mergeTree(t1->right, t2->right);
	return root;
}

//判断是否是二叉搜索树
vector<int> vec;
void traversal(TreeNode* root) {
	if (root == NULL) return;
	traversal(root->left);
	vec.push_back(root->val); // 将⼆叉搜索树转换为有序数组
	traversal(root->right);
}
bool isValidBST(TreeNode* root) {
	vec.clear(); // 不加这句在leetcode上也可以过，但最好加上
	traversal(root);
	for (int i = 1; i < vec.size(); i++) {
		// 注意要⼩于等于，搜索树⾥不能有相同元素
		if (vec[i] <= vec[i - 1]) return false;
	}
	return true;
}

int main(int argc, char** argv)
{
	vector<int> invec = { 1,2,3,4,5,6,7};
	TreeNode* root = createBiTree(invec, 0);
	for (unsigned int i = 0; i < invec.size(); i++)
	{
		cout << invec[i] << " ";
	}
	vector<int> outvec; 

	//递归法先序遍历
	traversal(root, outvec);

	//迭代法先序遍历
	outvec.clear();
	outvec = preorderTraversal(root);

	//层序遍历
	outvec.clear();
	outvec = levelOrder(root);

	//翻转二叉树
	outvec.clear();
	invertTree(root);
	invertTree2(root);
	invertTree3(root);
	outvec = levelOrder(root);

	//判断二叉搜索树
	cout << "root是否是二叉搜索树："<< isValidBST(root) << endl;

	for (unsigned int i = 0; i < outvec.size(); i++)
	{
		cout << outvec[i]<<" ";
	}
	system("pause");
	return 0;
}

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