C++ Programming Code Examples
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Check if any Graph is Possible to be Constructed for a Given Degree Sequence
/* Check if any Graph is Possible to be Constructed for a Given Degree Sequence
- This algorithm checks whether a undirected graph can be generated from a given degree sequence.
- The graph should not have a self-edge and multiple edges.
- The time complexity of this algorithm is O(v*v).
- This algorithm takes the input of the number of vertexes and their corresponding degree.
- It Checks various constraints and tries to build the graph.
- If it fails, no valid graph can be created from the given sequence.
- Exit. */
#include<iostream>
#include<iomanip>
using namespace std;
// A function to print the adjacency matrix.
void PrintMat(int mat[][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";
// Print 1 if the corresponding vertexes are connected otherwise 0.
for(i = 0; i < n; i++)
{
cout<<setw(4)<<"("<<i+1<<")";
for(j = 0; j < n; j++)
{
cout<<setw(5)<<mat[i][j];
}
cout<<"\n\n";
}
}
int main()
{
int NOV, i, j, AdjMat[20][20] = {0};
cout<<"Enter the number of vertex in the graph: ";
cin>>NOV;
int degseq[NOV];
// Take input of the degree sequence.
for(i = 0; i < NOV; i++)
{
cout<<"Enter the degree of "<<i+1<<" vertex: ";
cin>>degseq[i];
}
for(i = 0; i < NOV; i++)
{
for(j = i+1; j < NOV; j++)
{
// For each pair of vertex decrement the degree of both vertex.
if(degseq[i] > 0 && degseq[j] > 0)
{
degseq[i]--;
degseq[j]--;
AdjMat[i][j] = 1;
AdjMat[j][i] = 1;
}
}
}
PrintMat(AdjMat, NOV);
}
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