树的遍历 非递归

之前写过一个层序遍历的笔记，今天写了下前中后序遍历

#include <stdio.h>
#include <malloc.h>
#define SIZE 20

typedef struct Node *n_pointer;
typedef struct Node{
		n_pointer left;
		n_pointer right;
		int       key;
};

int top = -1;//init stack
n_pointer stack[SIZE];
int is_empty()
{	
	return top == -1;
}
void input(n_pointer *root, int item)
{
	if(*root){
		if(item < (*root)->key)
			input(&((*root)->left), item);
		else if(item > (*root)->key)
			input(&((*root)->right), item);
		else
			printf("The same value \n");
	}else{
		n_pointer ptr = (n_pointer)malloc(sizeof(struct Node));
		ptr->key = item;
		ptr->left = NULL;
		ptr->right = NULL;
		(*root) = ptr;
	}
}
//递归版本，验证非递归版本
void print_tree(n_pointer root)
{
	if(root){
		print_tree(root->left);
		printf("%d  ", root->key);
		print_tree(root->right);
	}
	else 
		return;
}
void pre_order(n_pointer root)
{
	if(root){
		n_pointer ptr;
		stack[++top] = root;
		while(!is_empty()){
			ptr = stack[top--];//stack decrease
			printf("%d  ", ptr->key);
			if(ptr->right){
				stack[++top] = ptr->right;
			}
			if(ptr->left){
				stack[++top] = ptr->left;
			}
		}
	}
	else 
		return;
}
void in_order(n_pointer root)
{
	if(root){
		n_pointer ptr = root;
		stack[++top] = root;
		while(ptr = ptr->left){
			stack[++top] = ptr;
		}//now, ptr is the lefist node
		while(!is_empty()){
			ptr = stack[top--];
			printf("%d  ", ptr->key);
			if(ptr->right){
				ptr = ptr->right;
				stack[++top] = ptr;
				while(ptr = ptr->left){
					stack[++top] = ptr;
				}
			}	
		}
	}
	else
		return;
}
void last_order(n_pointer root)
{
	
}
int main( void )
{
	n_pointer root = NULL;
	input(&root, 7);
	input(&root, 1);
	input(&root, 9);
	input(&root, 5);
	input(&root, 10);
	input(&root, 0);
	input(&root, 4);
	input(&root, 3);
	input(&root, 12);
	input(&root, 11);
	print_tree(root);
	printf("\n");
	in_order(root);
	return 0;
}