Two implementations of unweighted Charikar's algorithm for densest subgraph search.
Details of the algorithm can be found in:
Charikar, Moses. "Greedy approximation algorithms for finding dense components in a graph." Approximation Algorithms for Combinatorial Optimization. Springer Berlin Heidelberg, 2000. 84-95.
One implementation is based in dictionaries (O(mn)), another uses Fibonacci heaps O(m+n log(n)).
Referencies: