LeetCode Lowest Common Ancestor of a Binary Search Tree

Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.
According to the definition of LCA on Wikipedia: “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.

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/**
 * 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) {
        vector<TreeNode*> patha;
        vector<TreeNode*> pathb;
        dfs(root, patha, p);
        dfs(root, pathb, q);
        int alen = patha.size();
        int blen = pathb.size();
        TreeNode* comm = NULL;
        int i = 0;
        while (i < alen && i < blen && patha[i] == pathb[i]) {
            comm = patha[i++];
        }
        return comm;
    }
    
    void dfs(TreeNode* root, vector<TreeNode*>& path, TreeNode* target) {
        if (root == NULL || target == NULL) {
            return;
        }
        path.push_back(root);
        if (target->val < root->val) {
            dfs(root->left, path, target);
        } else if (target->val > root->val) {
            dfs(root->right, path, target);
        } else {
            return;
        }
    }
};