C++ Programming Code Examples
C++ > Computer Graphics Code Examples
Perform Edge Coloring to the Line Graph of an Input Graph
/* Perform Edge Coloring to the Line Graph of an Input Graph
- This algorithm performs edge coloring to the line graph of an input graph.
- A line graph can be generated from the given graph by assuming edge as vertex and vertex as edges between the vertex to form line graph.
- This algorithm takes the input of the number of vertexes and the number of edges in the graph.
- It takes the input of vertex pairs for the given number of edges.
- It generates a line graph for the given graph.
- Then for the generated line graph, it assigns a color to edges without assigning the same color to two adjacent edges.
- Exit. */
#include<iostream>
using namespace std;
// A function to generate line graph from a given graph.
int GenerateLineGraph(int edge[][2], char LineEdge[][3], int e)
{
int i, count = 0, j, NOV;
char ch;
// Loop to assign a valid color to every edge 'i'.
for(i = 0; i < e; i++)
{
for(j = i+1; j < e; j++)
{
// Check the colors of the edges adjacent to the edge i.
if(edge[j][0] == edge[i][0] || edge[j][0] == edge[i][1] || edge[j][1] == edge[i][0] || edge[j][1] == edge[i][1])
{
LineEdge[count][0] = 'a'+i;
LineEdge[count][1] = 'a'+j;
LineEdge[count][2] = 0;
count++;
}
}
}
NOV = count;
// Print the adjacency list representation of the graph.
cout<<"\n\nThe adjacency list representation for the given graph: ";
for(i = 0; i < e; i++)
{
count = 0;
// For each vertex print, its adjacent vertex.
ch = 'a'+i;
cout<<"\n\t"<<ch<<"-> { ";
for(j = 0; j < NOV; j++)
{
if(LineEdge[j][0] == i+'a')
{
cout<<LineEdge[j][1]<<" ";
count++;
}
else if(LineEdge[j][1] == i+'a')
{
cout<<LineEdge[j][0]<<" ";
count++;
}
else if(j == e-1 && count == 0)
cout<<"Isolated Vertex!";
}
cout<<" }";
}
return NOV;
}
// A function to color edges of the graph.
void EdgeColoring(char edge[][3], int e)
{
int i, col, j;
// Loop to assign a valid color to every edge 'i'.
for(i = 0; i < e; i++)
{
col = 1;
flag:
// Assign a color and then check its validity.
edge[i][2] = col;
for(j = 0; j < e; j++)
{
if(j == i)
continue;
// Check the colors of the edges adjacent to the edge i.
if(edge[j][0] == edge[i][0] || edge[j][0] == edge[i][1] || edge[j][1] == edge[i][0] || edge[j][1] == edge[i][1])
{
// If the color matches then goto line 11 and assign next color to the edge and check again.
if(edge[j][2] == edge[i][2])
{
col++;
goto flag;
}
}
}
}
}
int main()
{
int i, v, e, j, max = -1;
char ch = 'a';
// take the input of the number of vertex and edges.
cout<<"Enter the number of vertexes of the graph: ";
cin>>v;
cout<<"Enter the number of edges of the graph: ";
cin>>e;
int edge[e][2];
char LineEdge[e*e][3];
// Take the input of the adjacent vertex pairs of the given graph.
for(i = 0; i < e; i++)
{
cout<<"\nEnter the vertex pair for edge '"<<ch++<<"'";
cout<<"\nV(1): ";
cin>>edge[i][0];
cout<<"V(2): ";
cin>>edge[i][1];
}
// Generate line graph.
e = GenerateLineGraph(edge, LineEdge, e);
// Color The line graph.
EdgeColoring(LineEdge , e);
// Print the color of edges of line graph.
for(i = 0; i < e; i++)
cout<<"\nThe color of the edge between vertex V(1):"<<LineEdge[i][0]<<" and V(2):"<<LineEdge[i][1]<<" is: color"<<0+LineEdge[i][2]<<".";
}
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