【LeetCode 235_二叉搜索树】Lowest Common Ancestor of a Binary Search Tree

解法一：递归

 TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q)
 {
     if (root == NULL || p == NULL || q == NULL)
         return NULL;

     if (root->val > p->val && root->val > q->val)
         return lowestCommonAncestor(root->left, p, q);
     else if (root->val < p->val && root->val < q->val)
         return lowestCommonAncestor(root->right, p, q);
     return root;
 }

解法二：迭代

 TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q)
 {
     if (root == NULL || p == NULL || q == NULL)
         return NULL;

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