44 lines
911 B
Ruby
44 lines
911 B
Ruby
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#Given an unsorted array , sort the array when with only using the operation flip(a,i).
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#flip(a,i) means reversing the array a from index 0 to i
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#Time-complexity: O(n^2), In-place, Not-stable
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=begin
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Algorithm:Find the max element index max_i,flip(a,i),flip(0,len-1)(now max is at its right position),
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decrease len by 1
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=end
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def pancake_sort(a)
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n=a.length
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for i in n.downto(2)
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max_i=find_max(a,i)
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unless max_i == i-1
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flip(a,max_i)
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flip(a,i-1)
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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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def find_max(a,len)
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max_i=0
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i=1
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while i<len
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max_i=i if a[i]>a[max_i]
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i+=1
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end
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return max_i
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end
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def flip(a,len)
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start=0
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while start<len
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a[start],a[len]=a[len],a[start]
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start+=1
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len-=1
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end
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end
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pancake_sort([3,5,1,6,8,7,7,1,2,9]) #=> [1, 1, 2, 3, 5, 6, 7, 7, 8, 9]
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