28 lines
563 B
Ruby
28 lines
563 B
Ruby
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=begin
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Equilibrium index of an array is an index such that the sum of elements at lower indexes is equal to the sum of elements at higher indexes.
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For example, in an arrya A:
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A[]=[-7,1,5,2,-4,3,0]
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3 is an equilibrium index, because:
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A[0] + A[1] + A[2] = A[4] + A[5] + A[6]
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Time-complexity: O(n)
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Auxiliary-space: O(1)
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=end
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def find_equilibrium(a)
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len = a.length
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leftsum=0
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rightsum=0
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for x in a
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rightsum+=x
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end
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for i in 0...len
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rightsum-=a[i]
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if (leftsum == rightsum)
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return i
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end
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leftsum+=a[i]
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end
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return -1
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end
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