Suppose we are given a graph and are asked to find out the minimum size of the largest clique in the graph. A clique of a graph is a subset of a graph where every pair of vertices are adjacent, i.e. there exists an edge between every pair of vertices. Finding the largest clique in a graph is not possible in polynomial time, so given the number of nodes and edges of a small graph we shall have to find out the largest clique in it.
So, if the input is like nodes = 4, edges =4; then the output will be 2.
In the graph above, the maximum size of a clique is 2.
To solve this, we will follow these steps −
- Define a function helper() . This will take x, y
- ga := x mod y
- gb := y - ga
- sa := quotient of value of(x / y) + 1
- sb := quotient of value of(x / y)
- return ga * gb * sa * sb + ga *(ga - 1) * sa * sa / 2 + gb * (gb - 1) * sb * sb / 2
- i := 1
- j := nodes + 1
- while i + 1 < j, do
- p := i + floor value of((j - i) / 2)
- k := helper(nodes, p)
- if k < edges, then
- i := p
- otherwise,
- j := p
- return j
Example
Let us see the following implementation to get better understanding −
import math def helper(x, y): ga = x % y gb = y - ga sa = x // y + 1 sb = x // y return ga * gb * sa * sb + ga * (ga - 1) * sa * sa // 2 + gb * (gb - 1) * sb * sb // 2 def solve(nodes, edges): i = 1 j = nodes + 1 while i + 1 < j: p = i + (j - i) // 2 k = helper(nodes, p) if k < edges: i = p else: j = p return j print(solve(4, 4))
Input
4,4
Output
2