C Program for Traversing a Directed Graph through DFS recursively, with comments displayed in output

By | 22.06.2017

Directed Graph through DFS recursively with comments


Write a C Program for Traversing a Directed Graph through DFS recursively. Here’s simple Program for Traversing a Directed Graph through DFS recursively, with comments displayed in output.


Depth First Search (DFS)


Depth First Search (DFS) algorithm traverses a graph in a depthward motion and uses a stack to remember to get the next vertex to start a search, when a dead end occurs in any iteration.

It employs the following rules.

  • Rule 1 − Visit the adjacent unvisited vertex. Mark it as visited. Display it. Push it in a stack.
  • Rule 2 − If no adjacent vertex is found, pop up a vertex from the stack. (It will pop up all the vertices from the stack, which do not have adjacent vertices.)
  • Rule 3 − Repeat Rule 1 and Rule 2 until the stack is empty.

We shall not see the implementation of Depth First Traversal (or Depth First Search) in C programming language


Also Read : : C Program to implement BFS Algorithm for Connected Graph

Below is the source code for C Program for Traversing a Directed Graph through DFS recursively, with comments displayed in output which is successfully compiled and run on Windows System to produce desired output as shown below :


SOURCE CODE : :


/*  C Program for traversing a directed graph through DFS recursively,
   with comments displayed in the output  */

#include<stdio.h>
#define MAX 100

#define initial 1
#define visited 2
#define finished 3

int n;    /*Number of vertices in the graph */
int adj[MAX][MAX];
void create_graph( );

int state[MAX];

void DF_Traversal();
void DFS(int v);

int main()
{
        create_graph();
        DF_Traversal();
        return 0;

}/*End of main()*/

void DF_Traversal()
{
        int v;

        for(v=0; v<n; v++)
                state[v] = initial;

        printf("\nEnter starting vertex for Depth First Search : ");
        scanf("%d",&v);
        DFS(v);
        for(v=0; v<n; v++)
        {
                if(state[v] == initial)
                        DFS(v);
        }
        printf("\n");
}/*End of DF_Traversal( )*/

void DFS(int v)
{
        int i;
        state[v] = visited;
        printf("\nDFS(%d) called  \n", v);

        for(i=0; i<n; i++)
        {
                if( adj[v][i] == 1 )
                {
                        if(state[i] == initial )
                        {
                                printf("\n-- %d is adjacent to %d and initial\n", i, v);
                                DFS(i);
                        }
                }
        }
        state[v] = finished;
        printf("\nVertex %d finished\n", v);

}/*End of DFS()*/

void create_graph()
{
        int i,max_edges,origin,destin;

        printf("\nEnter number of vertices : ");
        scanf("%d",&n);
        max_edges = n*(n-1);

        for(i=1;i<=max_edges;i++)
        {
                printf("\nEnter edge %d( -1 -1 to quit ) : ",i);
                scanf("%d %d",&origin,&destin);

                if( (origin == -1) && (destin == -1) )
                        break;

                if( origin >= n || destin >= n || origin<0 || destin<0)
                {
                        printf("\nInvalid edge!\n");
                        i--;
                }
                else
                {
                        adj[origin][destin] = 1;
                }
        }
}

OUTPUT : :


/*  C Program for traversing a directed graph through DFS recursively,
   with comments displayed in the output  */

Enter number of vertices : 5

Enter edge 1( -1 -1 to quit ) : 0 1

Enter edge 2( -1 -1 to quit ) : 0 2

Enter edge 3( -1 -1 to quit ) : 0 3

Enter edge 4( -1 -1 to quit ) : 1 3

Enter edge 5( -1 -1 to quit ) : 3 4

Enter edge 6( -1 -1 to quit ) : 2 4

Enter edge 7( -1 -1 to quit ) : -1 -1

Enter starting vertex for Depth First Search : 0

DFS(0) called

-- 1 is adjacent to 0 and initial

DFS(1) called

-- 3 is adjacent to 1 and initial

DFS(3) called

-- 4 is adjacent to 3 and initial

DFS(4) called

Vertex 4 finished

Vertex 3 finished

Vertex 1 finished

-- 2 is adjacent to 0 and initial

DFS(2) called

Vertex 2 finished

Vertex 0 finished


Process returned 0

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