Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.

According to the : “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

_______6______       /              \    ___2__          ___8__   /      \        /      \   0      _4       7       9         /  \         3   5

For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {        if (!root)			return NULL;		TreeNode* tmp = root;		while (tmp)		{			if (tmp == p || tmp == q)			{//假设相等。则返回该结点				if (tmp == p)					return p;				else					return q;			}			else if ((p->val > tmp->val && q->val < tmp->val) || 				(p->val < tmp->val && q->val > tmp->val))			{//假设一个大于当前结点。一个小于当前结点。则返回当前结点				return tmp;			}			else if (p->val < tmp->val && q->val < tmp->val)			{//假设同一时候小于当前结点，则两个结点都在左子树其中				tmp = tmp->left;			}			else if (p->val > tmp->val && q->val > tmp->val)			{//假设同一时候大于当前结点，则两个结点都在右子树其中

tmp = tmp->right;			}		}		return NULL;    }};