题目：

题解：

class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        TreeNode* ancestor = root;
        while (true) {
            if (p->val < ancestor->val && q->val < ancestor->val) {
                ancestor = ancestor->left;
            }
            else if (p->val > ancestor->val && q->val > ancestor->val) {
                ancestor = ancestor->right;
            }
            else {
                break;
            }
        }
        return ancestor;
    }
};