Print Level Wise Binary Tree in C++ - c++

Question

The output is giving - Runtime Error (SIGSEGV). What could be the problem?
QUestion:
Given a binary tree, print the tree in level wise order.
For printing a node with data N, you need to follow the exact format -
N:L:x,R:y
wherer, N is data of any node present in the binary tree. x and y are the values of left and right child of node N. Print -1. if any child is null.
There is no space in between.
You need to print all nodes in the level order form in different lines.
Input format :
Elements in level order form (separated by space)
(If any node does not have left or right child, take -1 in its place)
Sample Input :
8 3 10 1 6 -1 14 -1 -1 4 7 13 -1 -1 -1 -1 -1 -1 -1
Sample Output :
8:L:3,R:10 3:L:1,R:6 10:L:-1,R:14 1:L:-1,R:-1 6:L:4,R:7 14:L:13,R:-1
4:L:-1,R:-1 7:L:-1,R:-1 13:L:-1,R:-1
Here is the code:
// Following is the Binary Tree node structure
/**************
class BinaryTreeNode {
public :
T data;
BinaryTreeNode<T> *left;
BinaryTreeNode<T> *right;
BinaryTreeNode(T data) {
this -> data = data;
left = NULL;
right = NULL;
}
};
***************/
void printLevelWise(BinaryTreeNode<int> *root) {
if(root == NULL){
return;
}
cout << root->data << ":";
queue<BinaryTreeNode<int>*> pendingNodes;
pendingNodes.push(root);
while(pendingNodes.size() != NULL){
BinaryTreeNode<int>* front = pendingNodes.front();
pendingNodes.pop();
if(front->left->data != -1){
cout << "L:" << front->left->data << ",";
pendingNodes.push(front->left);
}
else if(front->left->data == -1){
cout << "L:" << "-1" << ",";
}
if(front->right->data != -1){
cout << "R:" << front->right->data;
pendingNodes.push(front->right);
}
else if(front->left->data == -1){
cout << "R:" << "-1";
}
cout << endl;
}
/* Don't write main().
* Don't read input, it is passed as function argument.
* Print output and don't return it.
* Taking input is handled automatically.
*/
}

Answer 1

if(front->left->data != -1)
when your subtree not contain left node and you are checking left->data!=-1
thats why you are getting Runtime Error (SIGSEGV)
Use this code
/**************
class BinaryTreeNode {
public :
T data;
BinaryTreeNode<T> *left;
BinaryTreeNode<T> *right;
BinaryTreeNode(T data) {
this -> data = data;
left = NULL;
right = NULL;
}
};
***************/
void printLevelWise(BinaryTreeNode<int> *root) {
if(root == NULL){
return;
}
queue<BinaryTreeNode<int>*> pendingNodes;
pendingNodes.push(root);
while(pendingNodes.size() != NULL){
BinaryTreeNode<int>* front = pendingNodes.front();
pendingNodes.pop();
cout << front->data << ":";
if(front->left){
if(front->left->data != -1){
cout << "L:" << front->left->data << ",";
pendingNodes.push(front->left);
}
else{
cout << "L:" << "-1" << ",";
}
}
if(front->right){
if(front->right->data != -1){
cout << "R:" << front->right->data;
pendingNodes.push(front->right);
}
else{
cout << "R:" << "-1";
}
}
}
/* Don't write main().
* Don't read input, it is passed as function argument.
* Print output and don't return it.
* Taking input is handled automatically.
*/
}

Answer 2

As the description says, you should print "-1" if a child is null.
It does not say that you should print "-1" if the child's data is -1.
This would be the same as printing the data, so it would not be described as a special case.
(It is very important to read problem descriptions thoroughly. I think you're confusing this with the program's input format, which has -1 to indicate the absence of a child node, but that's not the input to your function.)
You need
if(front->left != nullptr) {
cout << "L:" << front->left->data << ",";
pendingNodes.push(front->left);
}
else {
cout << "L:" << "-1" << ",";
}
(You're also going to need to adjust how you print commas, but that's a different problem.)

Answer 3

void printLevelWise(BinaryTreeNode<int> *root)
{
if (root == NULL)
{
return;
}
queue<BinaryTreeNode<int> *> pendingNodes;
pendingNodes.push(root);
while (pendingNodes.size() != NULL)
{
BinaryTreeNode<int> *front = pendingNodes.front();
pendingNodes.pop();
cout << front->data << ":";
if (front->left)
{
if (front->left->data != -1)
{
cout << "L:" << front->left->data << ",";
pendingNodes.push(front->left);
}
}
else
{
cout << "L:"<< "-1"<< ",";
}
if (front->right)
{
if (front->right->data != -1)
{
cout << "R:" << front->right->data;
pendingNodes.push(front->right);
}
}
else
{
cout << "R:"<< "-1";
}
cout<<endl;
}
}