STL Queue error

Kalcor (188)
So I used STL queue inorder to do bfs on a binary search tree before and after deleting a node and it works well before deleting the node but after it just prints some weird ass numbers, then I tried the same code but with my own queue implementation and it worked fine? here is both:

my queue:
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#include <bits/stdc++.h>


#define fl(i,n)    for(int i = 0; i < n; i++)

#define ll   long long
#define nl   endl
#define pb   push_back
#define mp   make_pair
#define PII  pair<int,int>

#define EPS  1e-9
#define INF  1e9


using namespace std;

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


class Queue{
private:
    Queue* data;
    Queue *next;
public:
    void enqueue(Queue *&qhead, Queue *&qtail, Queue* x){
        Queue *temp = new Queue;
        temp->data = x;
        temp->next = nullptr;
        if(isEmpty(qhead)){
            qhead = temp;
            qtail = temp;
            return;
        }
        qtail->next = temp;
        qtail = temp;
    }

    void dequeue(Queue *&qhead, Queue *&qtail){
        if(isEmpty(qhead)) return;
        if(qhead == qtail){
            qhead = qtail = nullptr;
            return;
        }
        qhead = qhead->next;
    }

    Queue *peek(Queue *qhead){
        if(qhead == nullptr) return 0;
        return (qhead->data);
    }

    bool isEmpty(Queue *qhead){
        if(qhead == nullptr) return true;
        return false;
    }
};




node *Insert(node *root, int x){
if(root == nullptr){
    root = new node;
    root->data = x;
    root->left = nullptr;
    root->right = nullptr;
}
else if(x <= root->data){
    root->left = Insert(root->left, x);
}
else{
    root->right = Insert(root->right, x);
}
return root;
}



node *find_min_special(node *root){
if(root == nullptr) return nullptr;
else if(root->left == nullptr) return root;
return find_min_special(root->left);
}



node  *delete_node(node *root, int data){
if(root == nullptr) return root;
if(data < root->data) root->left = delete_node(root->left, data);
else if(data > root->data) root->right = delete_node(root->right, data);
else {
    //case 1 child or 0 children
    if(root->left == nullptr){
        node *temp = root->right;
        delete root;
        return temp;

    }
    else if(root->right == nullptr){
        node *temp = root->left;
        delete root;
        return temp;
    }
    node *temp = find_min_special(root->right);
    root->data = temp->data;
    root->right = delete_node(root->right, temp->data);//delete duplicate
}
return root;
}

void bfs(node *root){
Queue Q;
Queue *qhead = nullptr;
Queue *qtail = nullptr;

node *temp = root;
while(temp != nullptr){
    cout << temp->data << " ";
    if(temp->left != nullptr) Q.enqueue(qhead,qtail,(Queue*)temp->left);
    if(temp->right != nullptr) Q.enqueue(qhead,qtail,(Queue*)temp->right);

    temp = (node*)Q.peek(qhead);
    Q.dequeue(qhead,qtail);
}
cout << nl;
}




/*
        15
      /    \
    10     20
   /  \   /  \
  8    12 19 25
min(left most node), max(right most node), height = max(left height(1), right height(1))+1(back to root) = 2.
*/


int main()
{
    node *root = nullptr;

    root = Insert(root, 15);
    Insert(root, 10);
    Insert(root, 8);
    Insert(root, 12);
    Insert(root, 20);
    Insert(root, 19);
    Insert(root, 25);
    bfs(root);
    root = delete_node(root, 20);
    bfs(root);
    //cout << dfs_sum(root);
    //cout << dfs_inorder(root) << " " << leaves(root);
    //cout << Search(root, 25);
    //cout << find_min(root) << " " << height(root) << " " << find_max(root);



    return 0;
}



using stl queue:
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#include <bits/stdc++.h>


#define fl(i,n)    for(int i = 0; i < n; i++)

#define ll   long long
#define nl   endl
#define pb   push_back
#define mp   make_pair
#define PII  pair<int,int>

#define EPS  1e-9
#define INF  1e9


using namespace std;

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




node *Insert(node *root, int x){
if(root == nullptr){
    root = new node;
    root->data = x;
    root->left = nullptr;
    root->right = nullptr;
}
else if(x <= root->data){
    root->left = Insert(root->left, x);
}
else{
    root->right = Insert(root->right, x);
}
return root;
}



node *find_min_special(node *root){
if(root == nullptr) return nullptr;
else if(root->left == nullptr) return root;
return find_min_special(root->left);
}



node  *delete_node(node *root, int data){
if(root == nullptr) return root;
if(data < root->data) root->left = delete_node(root->left, data);
else if(data > root->data) root->right = delete_node(root->right, data);
else {
    //case 1 child or 0 children
    if(root->left == nullptr){
        node *temp = root->right;
        delete root;
        return temp;

    }
    else if(root->right == nullptr){
        node *temp = root->left;
        delete root;
        return temp;
    }
    node *temp = find_min_special(root->right);
    root->data = temp->data;
    root->right = delete_node(root->right, temp->data);//delete duplicate
}
return root;
}

void bfs(node *root){
queue<node*> q;

node *temp = root;
while(temp != nullptr){
    cout << temp->data << " ";
    if(temp->left != nullptr) q.push(temp->left);
    if(temp->right != nullptr) q.push(temp->right);

    temp = q.front();
    q.pop();
}
cout << nl;
}




/*
        15
      /    \
    10     20
   /  \   /  \
  8    12 19 25
min(left most node), max(right most node), height = max(left height(1), right height(1))+1(back to root) = 2.
*/


int main()
{
    node *root = nullptr;

    root = Insert(root, 15);
    Insert(root, 10);
    Insert(root, 8);
    Insert(root, 12);
    Insert(root, 20);
    Insert(root, 19);
    Insert(root, 25);
    bfs(root);
    root = delete_node(root, 20);
    bfs(root);
    //cout << dfs_sum(root);
    //cout << dfs_inorder(root) << " " << leaves(root);
    //cout << Search(root, 25);
    //cout << find_min(root) << " " << height(root) << " " << find_max(root);



    return 0;
}


it gave a runtime error on ideone.com but in my compiler printed a weird number which i guarantee is an address to some memory so i guess both errors are the same.


so what made stl queue output a runtime error but my queue implementation worked?
Last edited on
Peter87 (11254)
Line 86-87: You need to make sure not to call front() or pop() if the queue is empty.
Kalcor (188)
Thank you @peter :)
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