Cracking The Coding Interview 4.6

//原文：
//
//	Design an algorithm and write code to find the first common ancestor of two nodes in a binary tree. Avoid storing additional nodes in a data structure. NOTE: This is not necessarily a binary search tree.
//
//	译文：
//
//	写程序在一棵二叉树中找到两个结点的第一个共同祖先。不允许存储额外的结点。注意： 这里不特指二叉查找树。
//
#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <list>
using namespace std;

struct treenode
{
	char data;
	treenode * left;
	treenode * right;
	treenode * parent;
};

class tree
{
public:

	tree()
	{
		//root = create();
		root = NULL;
	}

	~tree()
	{
		/***清空二叉树***/
	}

	/***二叉排序树：插入。***/
	void insert(char *s)
	{
		if (s == NULL)
		{
			return;
		}

		int size = strlen(s);
		for (int i = 0; i<size; i++)
		{
			insert(&root, s[i], NULL);
		}
	}

	void levelOrder()
	{
		queue<treenode *> q;
		if (root != NULL)
		{
			q.push(root);
		}
		while(!q.empty())
		{
			treenode *t = q.front();
			cout<<t->data<<endl;
			q.pop();
			if (t->left != NULL)
			{
				q.push(t->left);
			}
			if (t->right != NULL)
			{
				q.push(t->right);
			}
		}
	}

	treenode * findNext(treenode *p)
	{

		if (p->right == NULL)
		{
			return p->parent;
		}
		else
		{
			treenode *s = p->right;
			while(s->left != NULL)
			{
				s = s->left;
			}
			return s;
		}
	}

	void preOrder(){	pOrder(root);}
	void inOreder(){	zOrder(root);}
	void postOreder(){  hOrder(root);}
	treenode *root;

	void findLCA(treenode *p,treenode *n1,treenode *n2,treenode **lca)
	{
		if (p==NULL || n1 ==NULL || n2 == NULL)
		{
			return;
		}
		if (p && father(p,n1) && father(p,n2))
		{
			*lca = p;
			findLCA(p->left,n1,n2,lca);
			findLCA(p->right,n1,n2,lca);

		}
	}

private:

	/***判断b是否为fa的子孙***/
	bool father(treenode * fa, treenode * b)
	{
		if (fa == NULL)
		{
			return false;
		}

		else if (fa == b)
		{
			return true;
		}
		else
		{
			return father(fa->left,b)||father(fa->right,b);
		}
	}

	void insert(treenode **p, char s, treenode *parent)
	{
		if (((*p) == NULL) && s != '\0')
		{
			*p = new treenode;
			(*p)->data = s;
			(*p)->left = NULL;
			(*p)->right = NULL;
			(*p)->parent = parent;
		}
		else
		{
			if ((*p)->data > s)
			{
				insert(&((*p)->left) , s, *p);
			}
			else
			{
				insert(&((*p)->right) , s, *p);
			}
		}
	}

	void pOrder(treenode *p)
	{
		if (p==NULL)
		{
			return;
		}

		cout<<p->data<<"  "<<endl;
		pOrder(p->left);
		pOrder(p->right);
	}

	void zOrder(treenode *p)
	{
		if (p==NULL)
		{
			return;
		}
		zOrder(p->left);
		cout<<p->data<<"  "<<endl;
		zOrder(p->right);
	}

	void hOrder(treenode *p)
	{
		if (p==NULL)
		{
			return;
		}
		hOrder(p->left);
		cout<<p->data<<"  "<<endl;
		hOrder(p->right);
	}
};

int main()
{
	/**非递归层次遍历*************************/
	tree s;
	char t[8] = "3289654";
	s.insert(t);
	//s.levelOrder();
	//treenode *p =s.findNext((s.root)->right);
	//cout<<p->data<<endl;
	treenode *lca;
	s.findLCA(s.root, s.root->right->right,s.root->right->left->left,&lca);
	cout<<lca->data<<endl;
	return 0;
}