i have this implementation of DFS:
void Graph::DFS(int start, vector<bool>& visited){
// Print the current node
cout << start << " ";
// Set current node as visited
visited[start] = true;
// For every node of the graph
for (int i = 0; i < v; i++) {
// If some node is adjacent to the current node
// and it has not already been visited
if (adj[start][i] == 1 && (!visited[i])) {
DFS(i, visited);
}
}
Instead of printing the travel i want it return the longest disntance from this start vertex.
what can i change into the code?
With a few changes you are able to do it, but it will be very slow.
int Graph::DFS(int start, vector<bool>& visited){
// Set current node as visited
visited[start] = true;
int out = 0;
// For every node of the graph
for (int i = 0; i < v; i++) {
// If some node is adjacent to the current node
// and it has not already been visited
if (adj[start][i] == 1 && (!visited[i])) {
out = max(out, DFS(i, visited) + 1);
}
}
visited[start] = false;
return out;
Related
Basically when we use DFS we just check if the adjacent nodes for a newly visited node have been already visited and they are not the parent node which made the DFS call for this node. If this is the case cycle is present.
I was using similar thing for BFS while keeping track of previous parent node and my logic doesn't seem to work. The test case on which my code is failing is too big to understand the problem. Can anyone let me know where my logic is broken? Thank you in advance
bool bfs(vector<int> adj[], bool isVisited[], int s, int V)
{
queue<int> q;
q.push(s);
isVisited[s] = true;
int parent = s;
int prevParent = -1;
while(q.empty() == false)
{
int u = q.front();
prevParent = parent;
parent = u;
q.pop();
for(int i = 0 ; i < adj[u].size() ; i++)
{
if(isVisited[adj[u][i]] == false)
{
isVisited[adj[u][i]] = true;
q.push(adj[u][i]);
// parent[][i]] = u;
}
else
{
if(adj[u][i] != prevParent)
return true;
}
}
}
return false;
}
bool isCycle(int V, vector<int> adj[]) {
// Code here
bool isVisited[V] = {false};
for(int i = 0 ; i < V ; i++)
{
if(isVisited[i] == false)
if(bfs(adj, isVisited, i, V) == true)
{
return true;
}
}
return false;
}
I was trying to reverse a linked list using recursion but when I tried to print out all the elements of the linked list at first it was printing out elements as expected but after printing out the last element it started printing the last and second last element repeatedly. I tried to debug it and I think the problem is that the last element is pointing towards the second last element whether it should be pointing towards NULL. I am not able to figure out what is wrong with my code so please help me out.
example- input 1,2,3,4,5,6
expected output 6,5,4,3,2,1
actual output 6,5,4,3,2,1,2,1,2 ...
#include<iostream>
using namespace std;
class node{
public:
int val;
node *next;
node(int val)
{
this->val = val;
this->next = NULL;
}
node(int val,node *next)
{
this->val= val;
this->next=next;
}
};
void insertAtTail(node *&head,int val){
node *n = new node(val);
if (head==NULL)
{
head = n;
return;
}
node *temp = head;
while (temp->next!=NULL)
{
temp = temp->next;
}
temp->next=n;
}
void display(node *head)
{
node *n = head;
while (n!=NULL)
{
cout << n->val << "->";
n = n->next;
}
cout << "NULL" << endl;
}
node* reverseRecursive(node *&head)
{
if (head == NULL || head->next==NULL)
{
return head;
}
node *nHead = reverseRecursive(head->next);
head->next->next = head;
head->next == NULL;
return nHead; // 1->2->3->4->5->6->NULL
}
int main()
{
node *head = NULL;
insertAtTail(head,1);
insertAtTail(head,2);
insertAtTail(head,3);
insertAtTail(head,4);
insertAtTail(head,5);
insertAtTail(head,6);
display(head);
node *newhead = reverseRecursive(head);
display(newhead);
return 0;
}
There is a bug in function reverseRecursive().
Line head->next == NULL; should be head->next = NULL;
node* reverseRecursive(node *&head)
{
if (head == NULL || head->next==NULL)
{
return head;
}
node *nHead = reverseRecursive(head->next);
head->next->next = head;
head->next == NULL; // <<< should be head->next = NULL;
return nHead; // 1->2->3->4->5->6->NULL
}
Not sure which compiler you were using, but this statement will typically generate a warning.
I want to implement the following function in PLSQL: https://www.geeksforgeeks.org/number-children-given-node-n-ary-tree/.
Is there a way to use queue.push as a function? It seems that it is not possible.
// Function to calculate number
// of children of given node
int numberOfChildren(Node* root, int x)
{
// initialize the numChildren as 0
int numChildren = 0;
if (root == NULL)
return 0;
// Creating a queue and pushing the root
queue<Node*> q;
q.push(root);
while (!q.empty()) {
int n = q.size();
// If this node has children
while (n > 0) {
// Dequeue an item from queue and
// check if it is equal to x
// If YES, then return number of children
Node* p = q.front();
q.pop();
if (p->key == x) {
numChildren = numChildren + p->child.size();
return numChildren;
}
// Enqueue all children of the dequeued item
for (int i = 0; i < p->child.size(); i++)
q.push(p->child[i]);
n--;
}
}
return numChildren;
}
I want to find first cycle in an undirected graph using BFS only(NOT DFS). All sources solved this problem with DFS but I have to find it using BFS. How can I find it? Thanks in advance!
Here below you will find the code to traverse a graph using BFS and find its cycles.
#include <stdio.h>
#include <queue>
using namespace std;
int nodes, edges, src;
int graph[100][100], color[100], prev[100];
const int WHITE = 0;
const int GRAY = 1;
const int BLACK = 2;
void print(int);
int main() {
printf("Nodes, edges, source? ");
scanf("%d %d %d ", &nodes, &edges, &src);
for(int i = 1; i <= edges; i++) {
printf("Edge %d: ", i);
int x, y;
scanf("%d %d", &x, &y);
graph[x][y] = 1;
}
//run BFS
queue<int> q; //create a queue
q.push(src); //1. put root node on the queue
do{
int u = q.front(); //2. pull a node from the beginning of the queue
q.pop();
printf("%d ", u); //print the node
for(int i = 1; i <= nodes; i++) { //4. get all the adjacent nodes
if((graph[u][i] == 1) //if an edge exists between these two nodes,
&& (color[i] == WHITE)) { //and this adjacent node is still WHITE,
q.push(i); //4. push this node into the queue
color[i] = GRAY; //color this adjacent node with GRAY
}
}
color[u] = BLACK; //color the current node black to mark it as dequeued
} while(!q.empty()); //5. if the queue is empty, then all the nodes havebeen visited
//find and print cycle from source
for(int i = 1; i <= nodes; i++) {
if(graph[i][src] == 1) {
print(i);
printf("%d\n\n", src);
}
}
return 0;
}
void print(int node) {
if(node == 0)
return;
print(prev[node]);
printf("%d -> ", node);
}
Also I recommend you to take a look at this brief and useful guide.
I have created this code, and when I run it, don't get any errors until the arrow leaves the screen (ie: (*I)->x>maxx), after which the O will randomly teleport (Well, I'm guessing its not random, but I'm trying to find a pattern to it).
EDIT: the random teleportation don't seem to occur if I move up, and if I move down, the O is teleported directly to the bottom. Also, a glitch has occured where the O becomes a '>'. (I am trying to figure out how that happens)
EDIT: the transform-into-'>' glitch occurs if the O is at the bottom right of the screen (player.x=9;player.y=9) and the sequence "wqs" is entered.
EDIT: I've removed the class declarations because I am fairly sure that the error is within the _move()s and check().
EDIT: The transform glitch appears to occur when 'wq' is typed, then any other character is entered (ie "skiping" the next move)
EDIT: The tranform glitch occurs when player.x=9; player.y=8; and then 'q' is pressed, the next move the player tranforms into a '>'
This is the code:
#include<vector>
#include<iostream>
#include<string>
using namespace std;
const int maxx = 10, maxy = 10; //two constants that show the size of the sector
char sector[maxx][maxy]; //array of characters used to display the sector
prgm player(0, 0, 'O'); //player definition at x0,y0,and displayed with 'O'
const int vsize = 1; //size of the enemy array (ie: how many enemies there will be
X1 a(9, 5, 'X', 10); //enemy "a", has a move function that moves it back and forth
virus * viral_data[vsize] = {&a}; //array of enemies used to set the sector
vector<antivirus*> antiviral_data; //vector of pointers to "antivirus" the weapon used
vector<antivirus*>::iterator I; //iterator for previous vector
void display() //function to display the sector
{
for(int i = 0; i < maxy; i++)
{
for(int j = 0; j < maxx; j++)
{
cout<<sector[j][i];
}
cout<<endl;
}
return;
}
void p_move() //function to get players input, then move the player or create "antivirus"
{
char dir;
cin>>dir;
switch(dir)
{
case 'w':
player.y--;
break;
case 'a':
player.x--;
break;
case 's':
player.y++;
break;
case 'd':
player.x++;
break;
case 'q':
antiviral_data.push_back(new aX1(player.x, player.y, '>')); //creates a new aX1 at the players position
break;
}
return;
}
void v_move() //uses the enemies move
{
for(int i = 0; i < vsize; i++)
{
viral_data[i]->move();
}
return;
}
void a_move() //uses the weapon (ie: moves the weapon forward)
{
for(I = antiviral_data.begin(); I < antiviral_data.end(); I++)
{
(*I)->move();
}
return;
}
void set() //sets the sector array (char)
{
for(int i = 0; i < maxy; i++)
{
for(int j = 0; j < maxx; j++)
{
sector[j][i] = ' '; makes the entire sector blank
}
}
sector[player.x][player.y]=player.sym; //sets the sector at the player's position to 'O'
for(int i = 0; i < vsize; i++)
{
sector[viral_data[i]->x][viral_data[i]->y] = viral_data[i]->sym; //sets the sector at each enemy's position to be 'X'
}
for(I = antiviral_data.begin(); I < antiviral_data.end(); I++)
{
sector[(*I)->x][(*I)->y] = (*I)->sym; //sets the sector at each weapon's position to be '>'
}
return;
}
void check() //prevents the player from moving off the screen, erases bullet if it moves of the screen (to prevent access to non-allocated memory)
{
if(player.x < 0)
{
player.x = 0;
}
if(player.y < 0)
{
player.y = 0;
}
if(player.x > (maxx-1))
{
player.x = (maxx-1);
}
if(player.y > (maxy-1))
{
player.y = (maxy-1);
}
//PROBLEM APPEARS TO OCCUR HERE
for(I = antiviral_data.begin(); I! = antiviral_data.end();)
{
if((*I)->x > maxx)
{
I = antiviral_data.erase(I);
}
else
{
I++;
}
}
//*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
return;
}
int main()
{
while(true)
{
set(); //set sector
display(); //display sector
p_move(); //player's move
v_move(); //enemy's move
a_move(); //bullet's move
check();//check moves
}
return 0;
}
In check(), the test
((*I)->x > maxx)
should be
((*I)->x >= maxx)
. This is an off-by-one error that lets the > get one square off the screen. When the display routine tries to display it, it clobbers the display symbol for the X.