In DFS, preference is given to child nodes, which means that after node a and node b are explored, and after node b and node c are explored, we hit a dead end and we backtrack to the previous level. This means that we go back to node b, and then to its next child, which is node c.
In BFS, the nodes are covered level by level, and preference is given to siblings. This means that after node a, nodes b and e are explored, and after that, nodes c, d, and f are explored, as indicated by the following diagram:
Figure 16
