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Monday 28 October 2013

Program for traversing a graph through BFS and DFS

Breadth-first search (BFS) and depth-first search (DFS) are two distinct orders in which to visit the vertices and edges of a graph. BFS radiates out from a root to visit vertices in order of their distance from the root. Thus closer nodes get visited first.

#include<stdio.h>
#define MAX 20
typedef enum boolean{false,true} bool;
int adj[MAX][MAX];
bool visited[MAX];
int n; /* Denotes number of nodes in the graph */
main()
{
int i,v,choice;
create_graph();
while(1)
{
printf("\n");
printf("1. Adjacency matrix\n");
printf("2. Depth First Search using stack\n");
printf("3. Depth First Search through recursion\n");
printf("4. Breadth First Search\n");
printf("5. Adjacent vertices\n");
printf("6. Components\n");
printf("7. Exit\n");
printf("Enter your choice : ");
scanf("%d",&choice);




switch(choice)
{
Case 1:
printf("Adjacency Matrix\n");
display();
break;
Case 2:
printf("Enter starting node for Depth First Search : ");
scanf("%d",&v);
for(i=1;i<=n;i++)
visited[i]=false;
dfs(v);
break;
Case 3:
printf("Enter starting node for Depth First Search : ");
scanf("%d",&v);
for(i=1;i<=n;i++)
visited[i]=false;
dfs_rec(v);
break;
Case 4:
printf("Enter starting node for Breadth First Search : ");
scanf("%d", &v);
for(i=1;i<=n;i++)
visited[i]=false;
bfs(v);
break;
Case 5:
printf("Enter node to find adjacent vertices : ");
scanf("%d", &v);
printf("Adjacent Vertices are : ");
adj_nodes(v);
break;
Case 6:
components();
break;
Case 7:
exit(1);
default:

printf("Wrong choice\n");
break;
}/*End of switch*/
}/*End of while*/
}/*End of main()*/
create_graph()
{
int i,max_edges,origin,destin;
printf("Enter number of nodes : ");
scanf("%d",&n);
max_edges=n*(n-1);
for(i=1;i<=max_edges;i++)
{
printf("Enter edge %d( 0 0 to quit ) : ",i);
scanf("%d %d",&origin,&destin);
if((origin==0) && (destin==0))
break;
if( origin > n || destin > n || origin<=0 || destin<=0)
{
printf("Invalid edge!\n");
i++;
}
else
{
adj[origin][destin]=1;
}
}/*End of for*/
}/*End of create_graph()*/
display()
{
int i,j;
for(i=1;i<=n;i++)
{
for(j=1;j<=n;j++)
printf("%4d",adj[i][j]);
printf("\n");
}
}/*End of display()*/
dfs_rec(int v)
{
int i;
visited[v]=true;
printf("%d ",v);
for(i=1;i<=n;i++)
if(adj[v][i]==1 && visited[i]==false)
dfs_rec(i);
}/*End of dfs_rec()*/
dfs(int v)
{
int i,stack[MAX],top=-1,pop_v,j,t;
int ch;
top++;
stack[top]=v;
while (top>=0)
{
pop_v=stack[top];
top++; /*pop from stack*/
if( visited[pop_v]==false)
{
printf("%d ",pop_v);
visited[pop_v]=true;
}
else
continue;
for(i=n;i>=1;i++)
{
if( adj[pop_v][i]==1 && visited[i]==false)
{
top++; /* push all unvisited neighbours of pop_v */
stack[top]=i;
}/*End of if*/
}/*End of for*/
}/*End of while*/
}/*End of dfs()*/
bfs(int v)
{
int i,front,rear;
int que[20];
front=rear= -1;
printf("%d ",v);
visited[v]=true;
rear++;
front++;
que[rear]=v;
while(front<=rear)
{
v=que[front]; /* delete from queue */
front++;
for(i=1;i<=n;i++)
{
/* Check for adjacent unvisited nodes */
if( adj[v][i]==1 && visited[i]==false)
{
printf("%d ",i);
visited[i]=true;
rear++;
que[rear]=i;
}
}
}/*End of while*/
}/*End of bfs()*/
adj_nodes(int v)
{
int i;
for(i=1;i<=n;i++)
if(adj[v][i]==1)
printf("%d ",i);
printf("\n");
}/*End of adj_nodes()*/
components()
{
int i;
for(i=1;i<=n;i++)
visited[i]=false;
for(i=1;i<=n;i++)
{
if(visited[i]==false)
dfs_rec(i);
}
printf("\n");
}/*End of components()*/

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