The Achilles heel of a simple digital tree is very poor memory utilization, especially when the N in N-ary (the degree or fanout of each branch) increases.

Enter the Judy Tree.

The Judy tree design was able to solve this problem. In fact a Judy tree is more memory-efficient than almost any other competitive structure (including a simple linked list). A highly populated linear array[] is the notable exception. Looking forward to implementing it!

Via : http://lambda-the-ultimate.org/node/741