递归插入二叉树（geeksforgeeks）

Question

I'm trying to implement the insertion function used on geeksforgeeks.com but am running into some problems trying to work it into my current code.

I have a vector with the data I need to put into the binary tree. I use this function to pass the numbers into the insertion function:

void populateTree(vector<string> dataVec) {
    for (int i = 0; i < dataVec.size(); i++) {
        insert(stoi(dataVec[i]), root);
    }
}

This is the insertion function:

node* insert(int x, node* node) {

    if (node == nullptr)
        return newNode(x);
    if (x < node->data)
        node->left = insert(x, node->left);
    else
        node->right = insert(x, node->right);

    return root;
}

New node function:

node* newNode(int num) {

node* temp = new node;
temp->data = num;
temp->left = temp->right = nullptr;
temp->level = 1;
return temp;

}

Root is a private member within the class which is initialized to nullptr. I'm not sure how I should go about making the first node that comes in from the vector as the root and then keep inserting things beginning from there recursively. Thanks!

Answer 1

The problem in your is related to use of pointer.

Instead of using node* insert(int x, node* node) you should use node* insert(int x, node** node) or node* insert(int x, node*& node) and adopt your code accordingly.

Following is corrected sample code. See it in execution here :

#include <iostream>
#include <vector>
using namespace std;

struct Node
{
    int val;
    Node* left;
    Node* right;

    Node(int v)
    {
        val = v;
        left = right = nullptr;
    }
};


class Tree
{
    Node* root;

    Tree()
    {
        root = nullptr;
    }

    public:

    static void insert(int x, Node*& node)
    {
        if (node == nullptr)
        {
            node = new Node(x);
        }
        else
        {
            if (x < node->val)
                insert(x, node->left);
            else
                insert(x, node->right);
        }
    }

    static Tree* populateTree(vector<string> dataVec)
    {
        Tree* t= new Tree();
        for (int i = 0; i < dataVec.size(); i++)
        {
            insert(stoi(dataVec[i]), t->root);
        }
        return t;
    }

    static void printTree(Node* node, string s)
    {
        if(node == nullptr) return;
        cout<<s<< "+"<<node->val <<endl;
        s += "----";
        printTree(node->left,s);
        printTree(node->right, s);
    }

    static void printTree(Tree* t)
    {
        if(t)
        {
            printTree(t->root, "");
        }
    }
};

int main() {
    Tree* t = Tree::populateTree({"70", "2", "7", "20", "41", "28", "20", "51", "91"});
    Tree::printTree(t);
    return 0;
}