Unexpected result of my DFS tree (C++) - c++

I have solved this problem!!! I found that if i have to use vector<Node*> children;. But I am not very sure the reason, can someone tell me why? Thanks:)
Question:
I use test.cpp to generate a tree structure like:
The result of (ROOT->children).size() is 2, since root has two children.
The result of ((ROOT->children)[0].children).size() should be 2, since the first child of root has two children. But the answer is 0, why? It really confuse for me.
test.cpp (This code is runnable in visual studio 2010)
#include <iostream>
#include <vector>
using namespace std;
struct Node {
int len;
vector<Node> children;
Node *prev;
Node(): len(0), children(0), prev(0) {};
};
class gSpan {
public:
Node *ROOT;
Node *PREV;
void read();
void insert(int);
};
int main() {
gSpan g;
g.read();
system("pause");
}
void gSpan::read() {
int value[4] = {1, 2, 2, 1};
ROOT = new Node();
PREV = ROOT;
for(int i=0; i<4; i++) {
insert(value[i]);
}
cout << "size1: " << (ROOT->children).size() << endl; // it should output 2
cout << "size2: " << ((ROOT->children)[0].children).size() << endl; // it should output 2
system("pause");
}
void gSpan::insert(int v) {
while(v <= PREV->len)
PREV = PREV->prev;
Node *cur = new Node();
cur->len = v;
cur->prev = PREV;
PREV->children.push_back(*cur);
PREV = cur;
}

The problem is that you children vector contains Node values rather than Node* pointers. While your access uses the root correctly, it finds only copies of the children you try to maintain. All of your nodes are also leaked.
You might want to use a std::vector<Node*> for your children and delete them at some point. The easiest way is probably to use a vector of smart pointers, e.g. a teference counted pointer, and have the smart pointer take care of the release.

Related

What does this strange number mean in the output? Is this some memory Location? [duplicate]

This question already has answers here:
Undefined, unspecified and implementation-defined behavior
(9 answers)
Closed 1 year ago.
The node Class is as follow:
class node
{
public:
int data; //the datum
node *next; //a pointer pointing to node data type
};
The PrintList Function is as follow:
void PrintList(node *n)
{ while (n != NULL)
{
cout << n->data << endl;
n = n->next;
}
}
If I try running it I get all three values (1,2,3) but I get an additional number as well which I'm unable to figure out what it represents, Can someone throw light on the same?
int main()
{
node first, second, third;
node *head = &first;
node *tail = &third;
first.data = 1;
first.next = &second;
second.data = 2;
second.next = &third;
third.data = 3;
PrintList(head);
}
I Know it can be fixed with
third.next = NULL;
But I am just curious what does this number represents in output, If I omit the above line
1
2
3
1963060099
As described in the comment by prapin, third.next is not initialized.
C++ has a zero-overhead rule.
Automatically initializing a variable would violate this rule as the value might be initialized (a second time) later on or never even be used.
The value of third.next is just the data that happened to live in the same memory location as third.next does now.
For this reason, it's recommended to always initialize your variables yourself.
It is better to initialize variables & it is better to use nullptr. Like that (See 1-3):
#include <iostream>
class node
{
public:
int data = 0; // 1
node* next = nullptr; // 2
};
void PrintList(node* n)
{
while (n != nullptr) // 3
{
std::cout << n->data << std::endl;
n = n->next;
}
}
int main()
{
node first, second, third;
node* head = &first;
node* tail = &third;
first.data = 1;
first.next = &second;
second.data = 2;
second.next = &third;
third.data = 3;
// third.next points to where?
PrintList(head);
}
Additional note:
I would prefer to use the STL container std::list:
#include <list>
#include <iostream>
std::list<int> int_list;
void PrintList()
{
for (auto i : int_list)
std::cout << i << std::endl;
}
int main()
{
int_list.push_back(1);
int_list.push_back(2);
int_list.push_back(3);
PrintList();
}
Or in case of list of node objects:
#include <list>
#include <iostream>
class node
{
public:
node(int data) : m_data{ data } {};
int m_data = 0;
// and maybe extra data-members
};
std::list<node> node_list;
void PrintList()
{
for (auto i : node_list)
std::cout << i.m_data << std::endl;
}
int main()
{
node_list.push_back(node(1));
node_list.push_back(node(2));
node_list.push_back(node(3));
PrintList();
}

Try tree inplementation

Try to make tree , have a some troubles, first it's print function - it's print not integers that i put, but print random numbers;
Another trouble its append child - its works only one times;
Will be happy if you will help me with this task.
And also give some good articles about linked lists, trees on c and c++;
#include <iostream>
#include <stdio.h>
using namespace std;
struct Node
{
void* m_pPayload;
Node* m_pParent;
Node* m_Children;
};
struct Person
{
int m_Id;
};
//typedef bool (*NodeComparator)(void* pValue, void* pPayload);
/*bool Comp(void* pValue, void* pPayload)
{
Person* pVal = (Person*)pValue;
Person* pPay = (Person*)pPayload;
if (pVal->m_Id == pPay->m_Id)
return true;
else
return false;
}
*/
Node* NewNode(void* pPayload)
{
Node* pNode = new Node;
pNode->m_pParent = nullptr;
pNode->m_Children = 0;
pNode->m_pPayload = pPayload;
return pNode;
}
Person* NewPerson(int id)
{
Person* p = new Person;
p->m_Id = id;
return p;
}
//Node* FindNode(Node* pParent, Node* m_pPayload, NodeComparator comparator);
void AppendChild(Node* pParent, Node* pNode)
{
if (pParent->m_Children == NULL)
pParent->m_Children = pNode;
}
void print(Node* head)
{
Node* current_node = head;
while (current_node != NULL)
{
printf("%d\n ", current_node->m_pPayload);
current_node = current_node->m_Children;
}
}
int main()
{
Node* T = new Node;
T = NewNode(NewPerson(5));
AppendChild(T, NewNode(NewPerson(11)));
AppendChild(T, NewNode(NewPerson(15)));
print(T);
}
printf("%d\n ", current_node->m_pPayload)
is incorrect. %d wants an integer and it's being given a pointer. The results will be unusual, and likely appear to be random garbage.
printf("%d\n ", ((Person*)current_node->m_pPayload)->m_Id);
^ ^
| Get id from Person
treat payload pointer as pointer to Person
will solve the immediate problem.
Your code actually seems to be pretty messed up with a lot of things going on, here sharing my own commented code from few years back, hope it helps
#include <bits/stdc++.h>
using namespace std;
// Single node representation
struct node {
int data;
node *left, *right;
};
// Declaring temp for refference and root to hold root node
node *root, *temp;
// This function only generates a node and return it to the calling function with data stored in it
node* generateNode(int data){
temp = new node();
temp->data = data;
temp->left = temp->right = NULL;
return temp;
}
// This function actually adds node to the tree
node* addNode(int data, node *ptr = root){
// If the node passed as ptr is NULL
if(ptr == NULL){
ptr = generateNode(data);
return ptr;
}
// Condition to check in which side the data will fit in the tree
else if(ptr->data < data)
//if its in right, calling this function recursively, with the right part of the tree as the root tree
ptr->right = addNode(data, ptr->right);
else
//In case the data fits in left
ptr->left = addNode(data, ptr->left);
//Note: if there is no data in left or roght depending on the data's valid position, this function will get called with NULL as second argument and then the first condition will get triggered
//returning the tree after appending the child
return ptr;
}
//Driver function
int main ()
{
int c, data;
for (;;){
cin >> c;
switch(c){
case 1:
cout << "enter data: ";
cin >> data;
//Updating root as the tree returned by the addNode function after adding a node
root = addNode(data);
break;
default:
exit(0);
break;
}
}
return 0;
}
Please find below a piece of code that should easily get you started. It compiles and it traverse the tree using recursion.
#include <iostream>
#include <vector>
#include <stdio.h>
using namespace std;
struct Node
{
int m_Id;
vector<Node*> m_Children;
Node(const int& id){
m_Id = id;
}
void AppendChild(Node* pNode) {
m_Children.push_back(pNode);
}
void Print() {
printf("%d\n ", m_Id);
}
};
void traverse(Node* head)
{
Node* current_node = head;
current_node->Print();
for(int i = 0; i<current_node->m_Children.size(); i++) {
traverse(current_node->m_Children[i]);
}
}
int main()
{
Node* T0 = new Node(0);
Node* T10 = new Node(10);
T10->AppendChild(new Node(20));
Node* T11 = new Node(11);
Node* T12 = new Node(12);
Node* T22 = new Node(22);
T22->AppendChild(new Node(33));
T12->AppendChild(T22);
T0->AppendChild(T10);
T0->AppendChild(T11);
T0->AppendChild(T12);
traverse(T0);
}
First for printing the node value
Talking about the current mistake that you had committed is in the above code is:
You have not mentioned its pointer to its child (specifically right or left). Due to which it is showing garbage value every time.
For e.g.: print( node->left);
Since you need to type caste it properly to show the data of data.
For e.g.: printf("%d\n ", ((Person*)current_node->m_pPayload)->m_Id);
There is a specific direction in which you want to print data. For trees, there are three directions in which you can print the data of the node and they are as follow:
Left order or Inorder traversal
Preorder traversal
Postorder traversal
This can give you better information about traversal.
Secondly for adding the node to a tree
This might help explain it better.

Segmentation fault (core dumped) while creating binary tree of given height

This is my first time working with trees. I wrote a c++ code, but it says Segmentation fault (core dumped) , As far as I searched, this error comes from accessing a memory location that may be NULL. I tried 'new' keyword as malloc() should be avoided in c++, But still I didn't get how to resolve this in my code.
# include<iostream>
using namespace std;
struct node
{
int data;
node *left;
node *right;
}*next;
int k=0;
void tree(int i,/*struct*/ node *next = new node)
{
++k; --i;
if (i==0)
return;
//next = new node;
next->data = k*k;
next->left = NULL;
next->right = NULL;
tree(i, next->left);
tree(i, next->right);
return ;
}
void display (node* next)
{
cout<<next->data<<" ";
if (next->left!=NULL)
{
display(next->left);
display(next->right);
}
}
int main()
{
int h;
cout<<"Enter the expected height of tree : ";
cin>>h;
node *root;
root = new node;
root->data=0;
root->left=NULL;
root->right=NULL;
tree(h, (root->left));
tree(h, (root->right));
cout<<root->data<<" ";
display(root->left);
display(root->right);
return 0;
}
There are serious problems with this code. In particular, here:
void display (node* next)
{
cout<<next->data<<" ";
if (next->left!=NULL)
{
...
}
}
You dereference next without ever checking to see whether it's null. And it will be null. That's enough to explain the error you see.
I say that it will be null because of this:
void tree(int i,/*struct*/ node *next = new node)
{
...
return ;
}
...
root->left=NULL;
...
tree(h, (root->left));
...
display(root->left);
The tree function takes its second argument by value-- that means that it does not change the value of root->left. You then call display with a null argument. I suspect that you think void tree(int i,/*struct*/ node *next = new node) means something other than what it actually means.
More fundamentally, you must review the two ways to pass an argument, by reference and by value.
More fundamentally still, you must start with a small, simple program and build up in small steps, rather than trying to write a big complex program all at once.
#include <iostream>
using namespace std;
struct node
{
int data;
struct node *left;
struct node *right;
};
void tree(int i, struct node **root, int k)
{
if (i < 1)
return;
*root = new struct node;
(*root)->data = k*k;
(*root)->left = NULL;
(*root)->right = NULL;
tree(i - 1, &((*root)->left), k + 1);
tree(i - 1, &((*root)->right), k + 1);
}
void display(struct node *root)
{
if (root == NULL)
return;
cout << root->data << " ";
if (root->left != NULL)
display(root->left);
if (root->right != NULL)
display(root->right);
}
int main()
{
struct node *root;
int h;
cout<<"Enter the expected height of tree : ";
cin>>h;
tree(h, &root, 0);
display(root);
return 0;
}
I think you should do some more read up on how pointers works: http://www.tutorialspoint.com/cprogramming/c_pointers.htm
When you where calling tree(h, root->left) you actually just send the pointers value "NULL" == 0x0. As you want to allocate memory for it you should send a reference to the pointer. Hence &root and &((*root)->left). In the display function you have to check for NULL values both for left and right.
The code above is only improved and doesn't handle any freeing of memory, to be able to do that, traverse the tree and use delete on all leafs and work you back to the root.

How to print the Data part of Linkedlist

Basically I want to print the data part of the Linked list which is basically an Integer pointer and I am assigning it an array at the time of creation, I want to print all the values of it how to do so ???
Thank you.
Here is my code
using namespace std;
struct Node{
Node *next;
int *data;
};
class DataLine{
private:
Node *first;
public:
DataLine(){
first=NULL;
}
void create_list(){
Node *temp=new Node;
int i=2;
int dat[5]={12,13,14,13,16};
temp->data=dat;
temp->next=NULL;
if(first==NULL){
//cout<<"hello 1"<<endl;
first=temp;
}
else{
Node *curr=first; //We are now doing trevercing so we are assigning the first to the node because we donot want to move the first bacuse link break if we move the first
while(curr->next!=NULL) //searching end of list
{
curr=curr->next; //Moving to the next node
}
curr->next=temp; //insert node
temp=NULL; //Making the temp enpty to use it for the new purpose
//delete temp;
}
}
void print_list()
{
Node *prnt=first; //We are now again want trevercing so we agin run the node by the new node
while(prnt!=NULL) //Checking the loop will run till it get the null in the node means its address part and data part both are nUll
{
for(int i=0;i<5;i++)
cout<<" ***** The "<<" node is "<<*(prnt->data+i)<<endl; //Printing the data
prnt=prnt->next; //Moving to the next node
}
}
};
int main(){
DataLine dl;
dl.create_list();
dl.print_list();
_getch();
return 0;
}
The idea of your void print_list(void) is correct but you can make it much cleaner, note however I changed your output to print a single node per line (change that back if you want). The structure of a for loop seems, to me, perfect for linked lists and keeps the linked list code our of the body of the loop.
void print_list(void) const
{
for (Node* p = first; p != NULL; p = p->next)
{
for (int i = 0; i < Node::unLength; ++i) std::cout << p->data[i] << ", ";
std::cout << std::endl;
}
}
However, as pointed out in some of the comments, there are other problems in your create list code. The way I would suggest to fix these (for this program) would be to redefine your structure to always hold a fixed number of integers.
struct Node
{
enum { unLength = 5 };
Node* next;
int data[unLength];
};
I have also added here a constant for the length of the array, since its bad practice to have magic numbers floating around your code, what happens if you mistype one of them?
Now in your void create_list() you can go:
void create_list()
{
Node* temp = new Node;
// Set the next node of temp
temp->next = NULL;
// Add some data to temp (we can't just assign the data pointer in C/C++)
int data[Node::unLength] = {0, 1, 2, 3, 4};
for (int i = 0; i < Node::unLength; ++i) temp->data[i] = data[i];
Node *p = first;
while (p != NULL) p = p->next;
p->next = temp;
}
There is no point setting temp to NULL since temp is deleted straight after the function returns. In your previous code you set the pointer in Node to data (temp->data=dat;, this doesn't work either since dat was deleted as soon as the function returned, you need to instead allocate memory and copy the values from dat which is what the for loop in the above code does.
For you class constructor (and destructor) I would suggest:
class DataLine
{
private:
Node* first;
public:
DataLine(void) : first(NULL) {}
~DataLine(void)
{
while (first != NULL)
{
Node *temp = first->next;
delete first;
first = temp;
}
}
You had the right idea, but there are a few subtle things about C/C++ that aren't obvious in higher level languages, such as copying arrays and the scope of variables.
If you are using C++ however, I would really suggest not worrying about linked lists, just create a std::vector, in C++ 11 something like the following might work (untested):
#include <vector>
#include <array>
int main(int argc, char** argv)
{
std::vector< std::array<int, 5> > myData;
myData.push_back({0, 1, 2, 3, 4});
myData.push_back({0, 1, 2, 3, 4});
myData.push_back({0, 1, 2, 3, 4});
for (const auto& i : myData)
{
for (int j : i) std::cout << j << ", ";
std::cout << std::endl;
}
return 0;
}

Attempting to create a pointer to previous object inside object

I'm attempting to create a vector of pointers to Nodes, where each node stores a pointer to the previous Node in the list.
I made a small test program to see if I could access a variable gscore in the previous object to the one I call.
#include <iostream>
#include <vector>
using namespace std;
struct Node
{
Node(int gscore1)
{
gscore = gscore1;
}
Node *previous;
int gscore;
};
int main()
{
std::vector<Node*> nodeVec;
Node *tempnode;
tempnode = new Node(10);
Node *tempnode2;
tempnode = new Node(11);
nodeVec.push_back(tempnode);
nodeVec.push_back(tempnode2);
nodeVec[1]->previous = tempnode;
cout << nodeVec[1]->previous->gscore << endl;
return 0;
}
However this results in a crash. What is the correct way to do this?
You never initialize tempnode2. You initialize tempnode twice.
int main()
{
std::vector<Node*> nodeVec;
Node *tempnode;
tempnode = new Node(10);
Node *tempnode2;
tempnode2 = new Node(11); // <<---- HERE
nodeVec.push_back(tempnode);
nodeVec.push_back(tempnode2);
nodeVec[1]->previous = tempnode;
cout << nodeVec[1]->previous->gscore << endl;
return 0;
}
Looks like a typing error. The third line in main() should be tempnode2 not tempnode.