print nodes at a distance 'k' from leaf nodes

nodesatdistk.cpp

#include<iostream>
#include<set>
#include<cstdlib>
using namespace std;

struct node{
int data;
struct node *left;
struct node *right;
};

struct node *newnode(int x)
{
 struct node* ptr=(struct node*)malloc(sizeof(struct node));
    ptr->data=x;
    ptr->left=NULL;
    ptr->right=NULL;
    return ptr;
}

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

struct node* par;
    if(root==NULL)
    {
        root=newnode(x);
        return root;
    }
    else
    {
        struct node *proot=root;
        while(proot!=NULL)
        {

            if(x<proot->data)
            {
                par=proot;
                proot=proot->left;

            }
            else
            {
                par=proot;
                proot=proot->right;

            }
        }
         if(x<par->data)
        par->left=newnode(x);
    else
        par->right=newnode(x);

        return root;
    }

}

void display(struct node *root)
{

    if(root==NULL)
        return;
    display(root->left);
    cout<<"\t"<<root->data;
    display(root->right);
}
static int index=0;
void nodesatdistk(struct node *root,int *ar,int index,set<int>&s,int k)
{
    if(root==NULL)
        return;
    ar[index++]=root->data;
    if(root->left==NULL&&root->right==NULL&&(index-k-1>=0))
    {
        int x=ar[index-k-1];//index is now root to leaf path length
        s.insert(x);
        return;
    }
    nodesatdistk(root->left,ar,index,s,k);
    nodesatdistk(root->right,ar,index,s,k);
}
int main()
{

     int x;
     struct node *root=NULL;
     int ar[5];
     set<int>st;
     set<int>::iterator it;
     while(1)
        {

            cin>>x;
            if(x==-1)
            break;

            root=insert(root,x);
        }

        display(root);
        cout<<endl;
        nodesatdistk(root,ar,index,st,1);
        for(it=st.begin();it!=st.end();it++)
        {
            cout<<*it<<"\t";
        }
}