Lectures12-part-09-algorithms-1

Howmanystepsdoesittakewhenlinearsearchisrun

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Unformatted text preview: … M(n) Input x; Find memory location i such that M(i)=x (or report that x is not in list) Linear_search (x) i = 0 WHILE i < n+1 IF M(i) = x then halt and output i ELSE i = i+1 Output “not in the list”. How many steps does it take when Linear_search is run? Binary Search Binary Search Assume sorted data M(0) … M(n) Binsearch (x) put left, right fingers on 0 and n let midpoint be the point halfway between. WHILE x not equal M(midpoint) IF M(midpoint) < x THEN move left finger to midpoint ELSE move right finger to midpoint set midpoint halfway between fingers END WHILE Binary Search Binary Search Assume sorted data M(0) … M(n) Binsearch (x) left = 0 right = n midpoint = (left + right) / 2 WHILE x notequal M(midpoint) IF M(midpoint) < x THEN left = midpoint ELSE right = midpoint midpoint = (left + right) / 2 END WHILE This actually has several bugs. Can you figure out what they are? stepping through binary search stepping through binary search left right midpoint Initial values 0 16 ? compute midpt 0 16 8 move left 8 16 8 compute midpt 8 16 12 move right 8 12 12 compute midpt 8 12 10 move right 8 10 10 compute midpt 8 10 9 ARRAY M( ) searching for 33 M(0) = 3 M(1) = 4 M(2) = 6 M(3) = 21 M(4) = 24 M(5) = 27 M(6) = 28 M(7) = 30 M(8) = 31 M(9) = 33 M(10)= 39 M(11)= 44 M(12)= 4...
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This document was uploaded on 04/02/2014.

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