#Data structure
###A collection of data structures.
##List
###1.sort
(n-1+(n-2)+.....+1)
=n(n-1)/2
=o(n)^2
###2.selection
(n-1)+(n-2)...+1
=o(n)^2
###3.bubble
###4.shell
##stack ###1.stack in order use a array with a pointer pointer to the top
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