LeetCode Lowest Common Ancestor of a Binary Tree

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.
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).”

        _______3______
       /              
    ___5__          ___1__
   /              /      
   6      _2       0       8
         /  
         7   4

For example, the lowest common ancestor (LCA) of nodes 5 and 1 is 3. Another example is LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.

/**
 * 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*> path1;
        vector<TreeNode*> path2;
        dfs(root, p, path1);
        dfs(root, q, path2);
        
        int pos = 0;
        int len = min(path1.size(), path2.size());
        TreeNode* comm = NULL;
        
        while (pos < len && path1[pos] == path2[pos]) {
            comm = path1[pos++];
        }
        
        return comm;
    }
    
    bool dfs(TreeNode* root, TreeNode* target, vector<TreeNode*>& path) {
        if (root == NULL) {
            return false;
        }
        path.push_back(root);
        if (root == target) {
            return true;
        }
        if (dfs(root->left, target, path)) {
            return true;
        }
        if (dfs(root->right, target, path)) {
            return true;
        }
        path.pop_back();
        return false;
    }
};