C++ Program to Perform Greedy Coloring

Here is a C++ Program to Perform Greedy Coloring

Algorithm:

Begin
Take the number of vertices and edges as input.
Create function greedyColoring() to assign color to vertices:
A) Assign the first color to first vertex.
B) Initialize the remaining vertices.
C) Declare a temporary array to store the available colors.
D) Assign color to the remaining vertices.
Print the solution.
End

Example Code

#include<bits/stdc++.h>
#include<iostream>
using namespace std;
int n,e,i,j;
vector<vector<int> > g;
vector<int> col;
bool visit[1001];
void greedyColoring()
{
col[0] = 0;
for (i=1;i<n;i++)
col[i] = -1;
bool unuse[n];
for (i=0;i<n;i++)
unuse[i]=0;
for (i = 1; i < n; i++)
{
for (j=0;j<g[i].size();j++)
if (col[g[i][j]] != -1)
unuse[col[g[i][j]]] = true;
int cr;
for (cr=0;cr<n;cr++)
if (unuse[cr] == false)
break;
col[i] = cr;
for (j=0;j<g[i].size();j++)
if (col[g[i][j]] != -1)
unuse[col[g[i][j]]] = false;
}
}
int main()
{
int a,b;
cout<<"Enter number of vertices and edges respectively:";
cin>>n>>e;
cout<<"\n";
g.resize(n);
col.resize(n);
memset(visit,0,sizeof(visit));
for(i=0;i<e;i++)
{
cout<<"\nEnter edge vertices of edge "<<i+1<<" :";
cin>>a>>b;
a--; b--;
g[a].push_back(b);
g[b].push_back(a);
}
greedyColoring();
for(i=0;i<n;i++)
{
cout<<"Vertex "<<i+1<<" is coloured with "<<col[i]+1<<"\n";
}
}

Output

Enter number of vertices and edges respectively:7
6
Enter edge vertices of edge 1 :4 5
Enter edge vertices of edge 2 :2 3
Enter edge vertices of edge 3 :1 1
Enter edge vertices of edge 4 :1 4
Enter edge vertices of edge 5 :6 7
Enter edge vertices of edge 6 :2 2
Vertex 1 is coloured with 1
Vertex 2 is coloured with 1
Vertex 3 is coloured with 2
Vertex 4 is coloured with 2
Vertex 5 is coloured with 1
Vertex 6 is coloured with 1
Vertex 7 is coloured with 2