非遞歸構造二叉樹

利用遞歸很容易就能夠構造二叉樹，但是利用非遞歸方法就不那麼容易。非遞歸方式構建二叉樹需要用到棧的結構，在這裏梳理一下思路。

#include <iostream>
#include <stack>
#include <string>

using namespace std;

class BiNode
{
public:
	BiNode() {};
	BiNode(char c) :val(c) {};
	char val;
	BiNode* left = NULL;
	BiNode* right = NULL;
};

BiNode* addTree(string str)
{
	BiNode* root = new BiNode(str[0]);
	stack<BiNode*> stk;
	stk.push(root);
	int id = 1;
	bool A = false;
	while (!stk.empty())
	{
		if (stk.top()->left == NULL && str[id - 1] != '#')
		{
			if (str[id] != '#')
			{
				BiNode* left = new BiNode(str[id]);
				stk.top()->left = left;
				stk.push(left);
			}
			id++;
		}
		else
		{
			if (stk.top()->right == NULL)
			{
				if (str[id] != '#')
				{
					BiNode* right = new BiNode(str[id]);
					stk.top()->right = right;
					stk.push(right);
				}
				else
				{
					stk.pop();
				}
				id++;
			}
			else
			{
				stk.pop();
			}
		}
	}
	return root;
}

void printTree(BiNode* root)
{
	if (root != NULL)
	{
		cout << root->val;
		if (root->left != NULL)
		{
			printTree(root->left);
		}
		if (root->right != NULL)
		{
			printTree(root->right);
		}
	}
}