Graph encoding schemes:

Adjacency list: Below we represent a graph of 6 nodes with an adjacency list.

{{{
1	-->	2	-->	4/
2	-->	5/		
3	-->	6	-->	5/
4	-->	2/		
5	-->	4/		
6	-->	6/		
}}}
Adjacency matrix: Below we reperesent the same graph of 6 nodes with an adjacency matrix.

{{{
	1	2	3	4	5	6
1	0	1	0	1	0	0
2	0	0	0	0	1	0
3	0	0	0	0	1	1
4	0	1	0	0	0	0
5	0	0	0	1	0	0
6	0	0	0	0	0	1
}}}
    Obviously the list saves space and the matrix saves access time.