Algorithm to find cliques of a given size k【O(n^k) time complexity】
We can find all the 2-cliques by simply enumerating all the edges. To find k+1-cliques, we can use the previous results. Compare all the pairs of k-cliques. If the two subgraphs have k-1 vertices in common and graph contains the missing edge, we can form a k+1-clique.