C++ Program to Implement all Forward Edges in a Graph

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This C++ program, using recursion, displays the number of forward edges in a graph. A forward edge is one in which a node points to one of it’s descendants.

Here is the source code of the C++ program to display the back edges as and when they are encountered. The C++ program is successfully compiled and run on DevCpp, a C++ compiler. The program output is also shown below.

  1. /*
  2.  * C++ Program to Implement all Forward Edges in a Graph
  3.  */
  4. #include<iostream>
  5. #include<conio.h>
  6. using namespace std;
  7. struct node_info
  8. {
  9.     int no;
  10.     int lv_time, st_time;
  11. }*q = NULL, *r = NULL;
  12. struct node
  13. {
  14.     node_info *pt;
  15.     node *next;
  16. }*top = NULL, *p = NULL, *np = NULL;
  17. struct node1
  18. {
  19.     node1 *link;
  20.     node_info *pt1;
  21. }*head = NULL, *m = NULL, *n = NULL, *np1 = NULL;
  22. int c = 0;
  23. void push(node_info *ptr)
  24. {
  25.     np = new node;
  26.     np->pt = ptr;
  27.     np->next = NULL;
  28.     if (top == NULL)
  29.     {
  30.         top = np;
  31.     }
  32.     else
  33.     {
  34.         np->next = top;
  35.         top = np;
  36.     }
  37. }
  38. node_info *pop()
  39. {
  40.     if (top == NULL)
  41.     {
  42.         cout<<"underflow\n";
  43.     }
  44.     else
  45.     {
  46.         p = top;
  47.         top = top->next;
  48.         return(p->pt);
  49.         delete(p);
  50.     }
  51. }
  52. void store(node_info *ptr1)
  53. {
  54.     np1 = new node1;
  55.     np1->pt1 = ptr1;
  56.     np1->link = NULL;
  57.     if (c == 0)
  58.     {
  59.         head = np1;
  60.         m = head;
  61.         m->link = NULL;
  62.         c++;
  63.     }
  64.     else
  65.     {
  66.         m = head;
  67.         np1->link = m;
  68.         head = np1;
  69.     }
  70. }
  71. int search(int j)
  72. {
  73.      node1 *t = head;
  74.      while (t != NULL)
  75.      {
  76.          if ((t->pt1)->no == j)
  77.          {
  78.              break;
  79.          }
  80.          else
  81.          {
  82.              t = t->link;
  83.              continue;
  84.          }
  85.      }
  86.      return (t->pt1)->lv_time;
  87. }             
  88. int present_in_stack(int j)
  89. {
  90.     int flag = 0;
  91.     p = top;
  92.     while (p != NULL)
  93.     {
  94.         if ((p->pt)->no == j)
  95.         {
  96.             flag = 1;
  97.             return flag;
  98.         }
  99.         p = p->next;
  100.     }
  101.     return flag;
  102. }
  103. void topo(int *v, int am[][8], int i)
  104. {
  105.     q = new node_info;
  106.     q->no = i;
  107.     q->st_time = c;
  108.     push(q);
  109.     v[i] = 1;
  110.     for (int j = 0; j < 8; j++)
  111.     {
  112.         if (am[i][j] == 0)
  113.             continue;
  114.         else if (am[i][j] == 1 && v[j] == 1 && !present_in_stack(j))
  115.         {
  116.             if (q->st_time < search(j))
  117.             {
  118.                 cout<<"\nForward Edge between "<<i<<" and "<<j<<endl;
  119.             }
  120.             continue;
  121.         }
  122.         else if (am[i][j] == 1 && v[j] == 0)
  123.         {
  124.             c++;
  125.             cout<<"\nForward Edge between "<<i<<" and "<<j<<endl;
  126.             topo(v,am,j);
  127.         }
  128.     }
  129.     c++;
  130.     q = pop();
  131.     q->lv_time = c;
  132.     store(q);
  133.     return;
  134. }
  135. int main()
  136. {
  137.     int v[8],am[8][8];
  138.     for (int i = 0; i < 8; i++)
  139.         v[i] = 0;
  140.     for (int i = 0; i < 8; i++)
  141.     {
  142.         cout<<"enter the values for adjacency matrix row:"<<i + 1<<endl;
  143.         for(int j = 0; j < 8; j++)
  144.         {
  145.             cin>>am[i][j];
  146.         }
  147.     }
  148.     topo(v,am,0);
  149.     getch();
  150. }

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Output
 
enter the values for adjacency matrix row:1
0
1
0
0
1
0
0
1
enter the values for adjacency matrix row:2
0
0
1
0
0
0
0
0
enter the values for adjacency matrix row:3
0
0
0
1
0
0
0
0
enter the values for adjacency matrix row:4
0
1
0
0
0
0
0
0
enter the values for adjacency matrix row:5
0
0
0
0
0
1
 
0
0
enter the values for adjacency matrix row:6
 
0
0
1
0
0
0
1
1
enter the values for adjacency matrix row:7
0
0
0
0
0
0
0
0
enter the values for adjacency matrix row:8
0
0
0
0
0
0
0
0
 
Forward Edge between 0 and 1
 
Forward Edge between 1 and 2
 
Forward Edge between 2 and 3
 
Forward Edge between 0 and 4
 
Forward Edge between 4 and 5
 
Forward Edge between 5 and 6
 
Forward Edge between 5 and 7
 
Forward Edge between 0 and 7

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn