Demonstrate Graph Traversal Strategies
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  Graph "testGraph 2-23-2018"
  n1 --> n2 
  n2 --> n1 n3 n4 
  n3 --> n1 n4 
  n4
  n5 --> n4 
  n6 --> n2 

  DFS_r_ltr starting at node n1
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   --> n1 --> n2 --> n3 --> n4

  DFS_r_ltr starting at node n1 and walking all
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   --> n1 --> n2 --> n3 --> n4 --> n5 --> n6

  DFS_r_ltr starting at node n3
 -------------------------------
   --> n3 --> n1 --> n2 --> n4

  DFS_r_ltr starting at node n3 and walking all
 -----------------------------------------------
   --> n3 --> n1 --> n2 --> n4 --> n5 --> n6

  DFS_r_ltrbtt starting at node n3
 ----------------------------------
   --> n4 --> n2 --> n1 --> n3

  DFS_r_rtl starting at node n3
 -------------------------------
   --> n3 --> n4 --> n1 --> n2

  DFS_s_ltr starting at node n3
 -------------------------------
   --> n3 --> n1 --> n2 --> n4 --> n4

  DFS_s_rtl starting at node n3
 -------------------------------
   --> n3 --> n4 --> n1 --> n2

  BFS_q starting at node n3
 ---------------------------
   --> n3 --> n1 --> n4 --> n2