Level order traversal of binary search tree - c

Question

I was trying to implement level order traversal of binary search tree using linked list implementation of queue.
I have checked the binary search tree implementation and it is fine.
The linked list implementation of queue is also correct.
Here i am trying to visit the node and enqueue its children to the queue.
and then use the pop function to actually visit the node.
This is being done via a recursive call in the end.
When i run the following code i am getting the output in different order.
// Trees
#include <stdio.h>
#include <stdlib.h>
//Node declaration for binary search tree
struct node
{
int data;
struct node *left;
struct node *right;
};
// LINKED LIST BASED IMPLEMENTATION OF QUEUE
struct qnode
{
struct node *data;
struct qnode *next;
};
struct qnode *head = NULL;
void insertq (struct node *); //This function enqueue node in the queue.
struct node *pop (); // dequeue function
//The function declaration for level order traversal.
void leorder ();
struct node *make (int);
struct node *insert (struct node *, int);
void
main ()
{
struct node *root = NULL;
root = insert (root, 10);
root = insert (root, 9);
root = insert (root, 8);
root = insert (root, 5);
root = insert (root, 2);
root = insert (root, 4);
root = insert (root, 3);
root = insert (root, 6);
root = insert (root, 7);
root = insert (root, 1);
insertq (root); //Insertion of first root.
leorder ();
}
//The program that makes nodes for the bst.
struct node* make(int x){
struct node* temp = (struct node*)malloc(sizeof(struct node));
temp->data = x;
temp->left = NULL;
temp->right = NULL;
return temp;
};
//The node insertion function.(BINARY SEARCH TREE)
struct node* insert(struct node* root,int x){
if(root == NULL){
root = make(x);
}
else{
if(x <= root->data){
root->left = insert(root->left,x);
}
else{
root->right = insert(root->right,x);
}}
return root;
}
// This function will insert node in the queue.
void insertq(struct node* x){
if(head == NULL){
struct qnode* temp = (struct qnode*)malloc(sizeof(struct qnode));
temp->data = x;
temp->next = NULL;
head = temp;
}
else{
struct qnode* temp = (struct qnode*)malloc(sizeof(struct qnode));
temp->data = x;
temp->next = head;
head = temp;
}
}
struct node* pop(){
struct node* r;
if(head == NULL){
return NULL;
}
else{
struct qnode* pt;
pt = head;
head = head->next;
r = pt->data;
free(pt);
return r;
}
}
// dequeue function.
struct node* pop(){
struct node* r;
if(head == NULL){
return NULL;
}
else{
struct qnode* pt;
pt = head;
head = head->next;
r = pt->data;
free(pt);
return r;
}
}
// Function to print tree in level order.
void leorder(){
struct node* popped;
popped = pop();
printf("%d ",popped->data);
if(popped != NULL){
if(popped->left != NULL){
insertq(popped->left);
}
if(popped->right != NULL){
insertq(popped->right);
}
leorder();
}
}

Answer 1

Right now, you insert at the head, and you remove at the head. This means you have a stack (last in, first out), not a queue (first in, first out).
Add a tail pointer, and remove from the opposite end that you add. If you add at the head, remove from the tail, or vice-versa.