C++ Program to Generate a Graph for a Given Fixed Degree Sequence

This is a C++ program represents a undirected graph for the given degree sequence. The time complexity of this algorithm is O(v*v) and it does not include self-edge and multiple edges.

Algorithm

Begin
   To create the graph,
   Create the first loop to connect each vertex ‘i’.
   Create second nested loop to connect the vertex ‘i’ to every valid vertex ‘j’, next to it.
   If the degree of vertex ‘i’ and ‘j’ are more than zero, then connect them.
   Print the adjacency matrix using PrintMatrix().
End

Example Code

#include<iostream>
#include<iomanip>
using namespace std;
void PrintMatrix(int matrix[][20], int n) {
   int i, j;
   cout<<"\n\n"<<setw(3)<<" ";
   for(i = 0; i < n; i++)
   cout<<setw(3)<<"("<<i+1<<")";
   cout<<"\n\n";
   for(i = 0; i < n; i++) {
      cout<<setw(4)<<"("<<i+1<<")";
      for(j = 0; j < n; j++) {
         cout<<setw(5)<<matrix[i][j];
      }
      cout<<"\n\n";
   }
}
int main() {
   int N, i, j, AdjMat[20][20] = {0};
   cout<<"Enter the number of vertex in the graph: ";
   cin>>N;
   int degseq[N];
   for(i = 0; i < N; i++) {
      cout<<"Enter the degree of "<<i+1<<" vertex: ";
     cin>>degseq[i];
   }
   for(i = 0; i < N; i++) {
      for(j = i+1; j < N; j++) {
         (degseq[i] > 0 && degseq[j] > 0) {
            degseq[i]--;
            degseq[j]--;
            AdjMat[i][j] = 1;
            AdjMat[j][i] = 1;
         }
      }
   }
   PrintMatrix(AdjMat, N);
}

Output

Enter the number of vertexes of the graph: 5
Enter the number of edges of the graph: 4
Enter the vertex pair for edge 1
V(1): 2
V(2): 1
Enter the vertex pair for edge 2
V(1): 3
V(2): 2
Enter the vertex pair for edge 3
V(1): 1
V(2): 1
Enter the vertex pair for edge 4
V(1): 3
V(2): 1
(1) (2) (3) (4) (5)
(1) 0 1 1 1 1
(2) 1 0 0 1 0
(3) 1 0 0 0 0
(4) 1 1 0 0 1
(5) 1 0 0 1 0