leetcode 235. 二叉搜尋樹的最近公共祖先

利用二叉搜尋樹的特性左子樹的值都比根節點小，右子樹的值都比根節點大這一特點來做就好了

/**
 * 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) 
{
    while(root)
    {
        if(root->val>p->val&&root->val>q->val)
        {
            root=root->left;
        }
        else if(root->val<p->val&&root->val<q->val)
        {
            root=root->right;
        }
        else
            return root;
    }
    return NULL;
}
};