Most of the data structures we have looked at so far have been devoted to keeping a collection of elements in some linear order.

Trees   

Trees are the most common non-linear data structure in computer science.

• Useful in representing things that naturally occur in hierarchies
  • (e.g., many company organization charts are trees)
• and for things that are related in a “is-composed-of” or “contains” manner
  • (e.g., this country is composed of states, each state is composed of counties, each county contains cities, each city contains streets, etc.)

Trees also turn out to be exceedingly useful in implementing fast searching and insertion.

• Properly implemented, a tree can be both searched and inserted into in O(log N) time.

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