二叉树的前序中序后序遍历和层次遍历（递归和非递归方式）

结构体

typedef struct BTNode
{
	char data;
	struct BTNode *lchild;
	struct BTNode *rchild;
}BTNode;

利用栈实现前序遍历

void preordernoRecusion(BTNode *bt)      //栈实现前序遍历 
{
	if(bt!=NULL)
	{
	BTNode *Stack[maxSize];
	int top=-1;
	BTNode *p;
	Stack[++top]=bt;
	while(top!=-1)	
		{
			p=Stack[top--];
			printf("%c ",p->data);
			if(p->rchild!=NULL)
				Stack[++top]=p->rchild;
			if(p->lchild!=NULL)
				Stack[++top]=p->lchild;	
		}
	}
}

利用栈实现中序遍历

void inordernoRecursion(BTNode *bt)       //栈实现中序遍历 
{
	if(bt!=NULL) 
	{
	BTNode *Stack[maxSize];
	int top=-1;
	BTNode *p;
	p=bt;
	while(top!=-1||p!=NULL)
	{
		
		while(p!=NULL)
		{
			Stack[++top]=p;
			p=p->lchild;
		}
		if(top!=-1)
		{
			p=Stack[top--];
			printf("%c ",p->data);
			p=p->rchild;
		}
	  } 
	}	
}

双栈后序遍历

void postordernoRecursion(BTNode *bt)    //双栈实现后序遍历 
{
	if(bt!=NULL)
	{
		BTNode *stack1[maxSize];int top1=-1;
		BTNode *stack2[maxSize];int top2=-1;
		BTNode *p;
		stack1[++top1]=bt;
		while(top1!=-1)
		{
		p=stack1[top1--];
		stack2[++top2]=p;
		if(p->lchild!=NULL)
			stack1[++top1]=p->lchild;
		if(p->rchild!=NULL)
			stack1[++top1]=p->rchild;						
		}		
	while(top2!=-1)
			{
			p=stack2[top2--];
			printf("%c ",p->data);
			}
	} 
}

队列实现层次遍历

void level(BTNode *p)      //层次遍历 
{
	BTNode *que[maxSize];
	int front,rear;
	front=rear=0;
	BTNode *q;
	if(p!=NULL)
	{
		rear=(rear+1)%maxSize;
		que[rear]=p;
		while(front!=rear)
		{
			front=(front+1)%maxSize;
			q=que[front];
			printf("%c ",q->data);
			if(q->lchild!=NULL)
			{ 
				rear=(rear+1)%maxSize;
				que[rear]=q->lchild;
			} 
			if(q->rchild!=NULL)
			{ 
				rear=(rear+1)%maxSize;
				que[rear]=q->rchild;
			} 
		}
	}
}

递归方式
https://blog.youkuaiyun.com/qq_44976531/article/details/108221025