Elemento más pequeño inmediato en un árbol N-ario

// C++ program to find immediate Smaller
// Element of a given element in a n-ary tree.
#include <bits/stdc++.h>
using namespace std;
  
// class of a node of an n-ary tree
class Node {
  
public:
    int key;
    vector<Node*> child;
  
    // constructor
    Node(int data)
    {
        key = data;
    }
};
  
// Function to find immediate Smaller Element
// of a given number x
void immediateSmallerElementUtil(Node* root, 
                            int x, Node** res)
{
    if (root == NULL)
        return;
  
    // if root is greater than res, but less
    // than x, then update res
    if (root->key < x)
        if (!(*res) || (*res)->key < root->key)
            *res = root; // Updating res
  
    // Number of children of root
    int numChildren = root->child.size();
  
    // Recursive calling for every child
    for (int i = 0; i < numChildren; i++)
        immediateSmallerElementUtil(root->child[i], x, res);
  
    return;
}
  
// Function to return immediate Smaller
// Element of x in tree
Node* immediateSmallerElement(Node* root, int x)
{
    // resultant node
    Node* res = NULL;
  
    // calling helper function and using
    // pass by reference
    immediateSmallerElementUtil(root, x, &res);
  
    return res;
}
  
// Driver program
int main()
{
    // Creating a generic tree
    Node* root = new Node(20);
    (root->child).push_back(new Node(2));
    (root->child).push_back(new Node(34));
    (root->child).push_back(new Node(50));
    (root->child).push_back(new Node(60));
    (root->child).push_back(new Node(70));
    (root->child[0]->child).push_back(new Node(15));
    (root->child[0]->child).push_back(new Node(20));
    (root->child[1]->child).push_back(new Node(30));
    (root->child[2]->child).push_back(new Node(40));
    (root->child[2]->child).push_back(new Node(100));
    (root->child[2]->child).push_back(new Node(20));
    (root->child[0]->child[1]->child).push_back(new Node(25));
    (root->child[0]->child[1]->child).push_back(new Node(50));
  
    int x = 30;
  
    cout << "Immediate smaller element of " << x << " is ";
    cout << immediateSmallerElement(root, x)->key << endl;
  
    return 0;
}