C++ Program to Check Cycle in a Graph using Topological Sort

C++Server Side ProgrammingProgramming

In a Directed Acyclic Graph, we can sort vertices in linear order using topological sort.

Topological sort is only work on Directed Acyclic Graph. In a Directed Acyclic Graph (DAG), there can be more than one topological sort.

We shall consider a C++ program, which will perform topological sort to check cycle in a graph.

For example

Algorithms

Topological Sort:
Begin
   Declare topo_sort(int *v, int T_S[][5], int i) function
      a = new NodeInfo.
      a->n = i
      a->S_Time = cn.
      Call push_node(a) function to insert data.
      v[i] = 1.
      for (int j = 0; j < 5; j++)
         if (T_S[i][j] == 0 || (T_S[i][j] == 1 && v[j] == 1)) then
            continue.
         else if(T_S[i][j] == 1 && v[j] == 0) then
            cn++.
            Call topo_sort(v,T_S, j) function.
      cn++.
      a = pop().
      a->L_Time = cn.
      Store_Node(a).
End.

Example

#include<iostream>
#include<conio.h>
using namespace std;
struct NodeInfo {
   int n;
   int L_Time, S_Time;
}
*a = NULL;
struct Node {
   NodeInfo *ptr;
   Node *nxt;
}
*t = NULL, *b = NULL, *npt = NULL;
struct Node_Link {
   Node_Link *lk;
   NodeInfo *ptr1;
}
*hd = NULL, *m = NULL, *n = NULL, *npt1 = NULL;
int cn = 0;
bool flag = false;
void push_node(NodeInfo *pt) { //insert data
   npt = new Node;
   npt->ptr = pt;
   npt->nxt = NULL;
   if (t == NULL) {
      t = npt;
   } else {
      npt->nxt = t;
      t = npt;
   }
}
NodeInfo *pop() {
   if (t == NULL) {
      cout<<"underflow\n";
   } else {
      b = t;
      t = t->nxt;
      return(b->ptr);
      delete(b);
   }
}
void Store_Node(NodeInfo *pt1) { //store data
   npt1 = new Node_Link;
   npt1->ptr1 = pt1;
   npt1->lk = NULL;
   if (cn == 0) {
      hd = npt1;
      m = hd;
      m->lk = NULL;
      cn++;
   } else {
      m = hd;
      npt1->lk = m;
      hd = npt1;
   }
}
void delete_node(int x) { //delete node
   m = hd;
   if ((m->ptr1)->n == x) {
      hd = hd->lk;
      delete(m);
   } else {
      while ((m->ptr1)->n != x && m->lk != NULL) {
         n = m;
         m = m->lk;
      }
      if ((m->ptr1)->n == x) {
         n->lk = m->lk;
         delete(m);
      } else if (m->lk == NULL) {
         flag = true;
         cout<<"There is no circle in this graph\n";
      }
   }
}
void topo_sort(int *v, int T_S[][5], int i) { //performing topological sort
   a = new NodeInfo;
   a->n = i;
   a->S_Time = cn;
   push_node(a);
   v[i] = 1;
   for (int j = 0; j < 5; j++) {
      if (T_S[i][j] == 0 || (T_S[i][j] == 1 && v[j] == 1))
         continue;
      else if(T_S[i][j] == 1 && v[j] == 0) {
         cn++;
         topo_sort(v,T_S,j);
      }
   }
   cn++;
   a = pop();
   a->L_Time = cn;
   Store_Node(a);
   return;
}
void topologic_sort(int *v, int T_S[][5], int i) {
   v[i] = 1;
   delete_node(i);
   for (int j = 0; j < 5; j++) {
      if (T_S[i][j] == 0 || (T_S[i][j] == 1 && v[j] == 1)) {
         continue;
      } else if(T_S[i][j] == 1 && v[j] == 0) {
         topologic_sort(v, T_S, j);
      }
   }
   return;
}
void Insert_Edge(int T_S[][5], int source, int destination) { // insert the value of edge.
   T_S[source][destination] = 1;
   return;
}
int main() {
   int v[5], T_S[5][5], T_S_N[5][5], cn = 0, a, b;
   for (int i = 0; i < 5; i++) {
      v[i] = 0;
   }
   for (int i = 0; i < 5; i++) {
      for (int j = 0; j < 5; j++) {
         T_S[i][j] = 0;
      }
   }
   while (cn < 5) {
      cout<<"Enter the source: ";
      cin>>a;
      cout<<"Enter the destination: ";
      cin>>b;
      cout<<endl;
      Insert_Edge(T_S, a, b);
      cn++;
   }
   topo_sort(v, T_S, 0);
   for (int i = 0; i < 5; i++) {
      v[i] = 0;
      for (int j = 0; j < 5; j++) {
         T_S_N[j][i] = T_S[i][j];
      }
   }
   if (hd != NULL) {
      topologic_sort(v, T_S_N, (hd->ptr1)->n);
      if (flag == false) {
         cout<<"There is a cycle in this graph...\n";
      }
   }
   getch();
}

Output

Enter the source: 0
Enter the destination: 1

Enter the source: 1
Enter the destination: 2

Enter the source: 2
Enter the destination: 3

Enter the source: 3
Enter the destination: 4

Enter the source: 4
Enter the destination: 0

There is a cycle in this graph...
raja
Published on 03-May-2019 12:32:55
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