68 lines
1.5 KiB
Ruby
68 lines
1.5 KiB
Ruby
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# Block swap algorithm for array rotation(Recursive)
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#Initialize A=[0..d-1], B=[d..size-1]
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#until size of A is equal to size of B
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# a) If A is shorter
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# 1. Divide B into Bl and Br such that Br is of same length as A.
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# 2. Swap A and Br to change ABlBr into BrBlA.
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# 3. Now A is at its final place, so recur on pieces of B.
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# b) If A is longer
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# 1. Divide A into Al and Ar such that Al is of same length as B.
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# 2. Swap Al and B to change AlArB into BArAl.
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# 3. Now B is at its final place, so recur on pieces of A.
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#Finally when A and B are of equal size, block swap them.
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# Recursive Approach
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#Driver function
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def rotate_array(a, d) #Input array "a" and rotation by "d" elemets
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finish =a.length-1
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block_swap(a,0,finish,d)
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end
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def block_swap(a,start,finish,d)
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n=finish-start+1
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if n>0
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if d>n
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d%=n
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end
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if d==0
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return a
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end
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if d==n-d
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swap(a,start,start+d,d)
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return a
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elsif d<n-d
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swap(a,start,finish-d+1,d)
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block_swap(a,start,finish-d,d)
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else
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swap(a,start,d,n-d)
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block_swap(a,n-d,n-1,(2*d)-n)
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end
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end
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return a
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end
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#Utility function for swapping
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def swap(a,start1,start2,d)
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for i in 0...d
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temp = a[start1+i]
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a[start1+i] = a[start2+i]
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a[start2+i] = temp
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end
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end
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rotate_array([1,2,3,4,5,6,7,8,9,10],6)
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