二叉树转双向链表

#include <iostream>

using namespace std;

// 树节点
struct node
{
	int val;
	struct node* left;
	struct node* right;
	node(int t)
	{
		val = t;
		left = right = 0;
	}
};

typedef struct node* link;

// 构造树
void insert_tree(link &h, int t)
{
	if (0 == h)
	{
		h = new node(t);
		return;
	}

	if (h->val > t) 
		insert_tree(h->left, t);
	else
		insert_tree(h->right, t);
}

// 二叉树转链表
link tree_to_listR(link &h, bool left)
{
	if (0 == h)
	{
		return 0;
	}


	link p = tree_to_list(h->left, true);
	link q = tree_to_list(h->right, false);
	
	if (0 == p && 0 == q) return h;
	
	link t, tt;
	if (0 != p)
	{
		tt = t = p;
		h->left = p;
		p->right = h;
	}

	if (0 != q)
	{
		tt = t = q;
		h->right = q;
		q->left = h;
	}

	while (tt->left != 0) tt = tt->left;
	while (t->right != 0) t = t->right; 
	if (left) return t;
	else return tt;
}

link tree_to_list(link &h)
{
	return tree_to_listR(h, false);
}
int main(int argc, char* argv[])
{
	link h = 0;
	insert_tree(h, 5);
	insert_tree(h, 6);
	insert_tree(h, 4);
	insert_tree(h, 3);
	insert_tree(h, 7);
	insert_tree(h, 8);
	insert_tree(h, 9);
	insert_tree(h, 2);
	insert_tree(h, 1);

	link head = tree_to_list(h);
	return 0;
}