此篇皆为leetcode、牛客中的简单题型和二叉树基础操作，无需做过多讲解，仅付最优解。有需要的小伙伴直接私信我~

目录

1.二叉树的节点个数

2.二叉树叶子节点个数

3.二叉树第K层节点个数

4.查找值为X的节点

5.leetcode——二叉树的最大深度

6.leetcode——单值二叉树

7.leetcode——相同的树

8.二叉树的前序遍历

9.二叉树的中序遍历 

10.二叉树的后序遍历 

11.二叉树的层序遍历

12.leetcode——另一棵树的子树

13.二叉树的构建及遍历 

14.leetcode——对称二叉树

1.二叉树的节点个数

int BinaryTreeSize(BTNode* root)
{
	return root == NULL ? 0 : 
           BinaryTreeSize(root->left) + 
           BinaryTreeSize(root->right) + 1;
}

2.二叉树叶子节点个数

int BinaryTreeLeafSize(BTNode* root)
{
	if (root == NULL)
		return 0;
	if (root->left == NULL && root->right == NULL)
		return 1;
	return BinaryTreeLeafSize(root->left) + BinaryTreeLeafSize(root->right);
}

3.二叉树第K层节点个数

int BinaryTreeLevelKSize(BTNode* root, int k)
{
	if (root == NULL)
		return 0;
	if (k == 1)
		return 1;
	return BinaryTreeLevelKSize(root->left, k - 1) + 
           BinaryTreeLevelKSize(root->right, k - 1);
}

4.查找值为X的节点

BTNode* BinaryTreeFind(BTNode* root, BTDataType data)
{
	if (root == NULL)
		return NULL;
	if (root->data == data)
		return root;

	BTNode* ret1 = BinaryTreeFind(root->left, data);
	if (ret1)
		return ret1;
	BTNode* ret2 = BinaryTreeFind(root->right, data);
	if (ret2)
		return ret2;
	return NULL;
}

5.leetcode——二叉树的最大深度

oj链接：二叉树的最大深度

int maxDepth(struct TreeNode* root) {
	if (root == NULL)
		return 0;

	int leftDepth = maxDepth(root->left);
	int rightDepth = maxDepth(root->right);

	return  (leftDepth > rightDepth ? leftDepth : rightDepth) + 1;
}

6.leetcode——单值二叉树

oj链接：单值二叉树

bool isUnivalTree(struct TreeNode* root)
{
	if (root == NULL)
	{
		return true;
	}
	if (root->left && root->val != root->left->val)
		return false;
	if (root->right && root->val != root->right->val)
		return false;
	return isUnivalTree(root->left) && isUnivalTree(root->right);
}

7.leetcode——相同的树

oj链接：相同的树

bool isSameTree(struct TreeNode* p, struct TreeNode* q) {
	if (p == NULL && q == NULL)
		return true;
	if (p == NULL || q == NULL)
		return false;
	if (p->val != q->val)
	{
		return false;
	}
	return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
}

8.二叉树的前序遍历

详细讲解：二叉树的前、中、后序遍历

void PrevOrder(BTNode* root)
{
	if (root == NULL)
	{
		printf("NULL ");
		return;
	}

	printf("%d ", root->data);//前序在前
	PrevOrder(root->left);
	PrevOrder(root->right);
}

9.二叉树的中序遍历 

void InOrder(BTNode* root)
{
	if (root == NULL)
	{
		printf("NULL ");
		return;
	}

	InOrder(root->left);
	printf("%d ", root->data);//中序在中
	InOrder(root->right);
}

10.二叉树的后序遍历 

void PostOrder(BTNode* root)
{
	if (root == NULL)
	{
		printf("NULL ");
		return;
	}

	PostOrder(root->left);
	PostOrder(root->right);
	printf("%d ", root->data);//后序在后
}

11.二叉树的层序遍历

详细讲解：看完这篇我不信你不会二叉树的层序遍历

//需自己实现队列的数据结构
void BinaryTreeLevelOrder(BTNode* root)
{
	Queue q;
	QueueInit(&q);

	if (root)
		QueuePush(&q, root);
	else
		return;

	while (!QueueEmpty(&q))
	{
		BTNode* front = QueueFront(&q);
		printf("%d ", front->data);
		
		QueuePop(&q);

		if(front->left)
			QueuePush(&q, front->left);
		if(front->right)
			QueuePush(&q, front->right);
	}

	printf("\n");
	QueueDestroy(&q);
}

12.leetcode——另一棵树的子树

oj链接：另一棵树的子树

//判断两树是否相同（复用“相同的树”解题代码）
bool isSametree(struct TreeNode* p,struct TreeNode* q)
{
    if(p==NULL && q==NULL)
        return true;
    if(p==NULL || q==NULL)
        return false;
        
    if(p->val != q->val)
        return false;

    return isSametree(p->left,q->left) && isSametree(p->right,q->right);
}

bool isSubtree(struct TreeNode* root, struct TreeNode* subRoot){
    if(root==NULL)
        return false;
    
    if(isSametree(root,subRoot))
        return true;

    return isSubtree(root->left,subRoot) || isSubtree(root->right,subRoot);
}

13.二叉树的构建及遍历 

题目链接：二叉树的遍历

注意：本题虽然是二叉树的遍历，但考查的却是如何通过数组的内容构建一棵二叉树。

#include <stdio.h>
#include <stdlib.h>

struct TreeNode {
    int val;
     struct TreeNode *left;
     struct TreeNode *right;
 };

struct TreeNode* rebuildTree(char* str,int* pi)
{
    if(str[*pi] == '#')
    {
        (*pi)++;
        return NULL;
    }
    struct TreeNode* root = (struct TreeNode*)malloc(sizeof(struct TreeNode));


    root->val = str[(*pi)++];
    root->left = rebuildTree(str,pi);
    root->right = rebuildTree(str,pi);

    return root;
}

void TreeDestory(struct TreeNode* root)
{
    if(root==NULL)
        return;
    
    TreeDestory(root->left);
    TreeDestory(root->right);

    free(root);
}

void InOrder(struct TreeNode* root)
{
	if (root == NULL)
	{
		return;
	}

	InOrder(root->left);
	printf("%c ", root->val);
	InOrder(root->right);
}
int main() {
    char str[100];
    scanf("%s",str);
    int i=0;
    struct TreeNode* root = rebuildTree(str,&i);
    InOrder(root);
    TreeDestory(root);
    return 0;
}

14.leetcode——对称二叉树

oj链接：对称二叉树

bool _isSymmetric(struct TreeNode* p, struct TreeNode* q)
{
	if (p == NULL && q == NULL)
		return true;
	if (p == NULL || q == NULL)
		return false;
	if (p->val != q->val)
		return false;

	return _isSymmetric(p->left, q->right) &&
		_isSymmetric(p->right, q->left);
}
bool isSymmetric(struct TreeNode* root) {
	return root == NULL ? 0 : _isSymmetric(root->left, root->right);
}