The graph is represented with nodes and pointers. In each node, it has
a unique ID, flag Visit and up to three pointers. The structure is showed
as follows:
class node {
public:
int ID;
bool Visit;
node *first, *second, *third;
}
In the class graph , we use an 1-D array nodelist to keep all the nodes. The total
number of node N are read from a file. E.g. the above graph has N = 5.
class graph { public:
node *nodelist;
graph(int N)
{
nodelist = new node[N+1];
}
void AddEdge(int n1, int n2);
bool CheckConnect(node *node1, node *node2);
}
The function AddEdge( ) is reading a pair of number (n1, n2) from file,
then adding the edge n1 -> n2 into the graph.
The function CheckConnect( ) is using DFS to find out whether there is
a path from node1 to node2.
Input File Format
The input file has the following format: The first number N is total number
of nodes. The second number V is total number of edges. Starting from the
third line, a pair of numbers (n1, n2) each line represents the edge n1 ->
n2. After V lines, there is a number T for the total number of tests, followed
by a pairs of node (t1, t2) each line for checking the connection between
t1 and t2.
5 // total number of nodes N
7 // total number of edges V
1 3
2 1
2 3
2 5
3 1
4 2
5 4
2 // total number of tests T
4 3
3 4
File operations in C++:
#include <fstream> //include this head file
ifstream infile("test1.txt"); //open a file for
reading
int num, num1, num2;
infile >> num; //read a integer from the file
infile >> num1 >> num2; // read two
integers at the same time
infile.close(); //close file before exit the program
Check Connection
Implement the CheckConnect( ) function using DFS. Output the result from
CheckConnect(node1, node2). If there is a path from node1 to node2, then
output "yes, node ## and node ## are connected.", else output "no, node ##
and node ## are disconnected.".
