题目：

题解：

struct TreeNode* lowestCommonAncestor(struct TreeNode* root, struct TreeNode* p, struct TreeNode* q) {
    struct 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;
}