28 lines
563 B
Ruby
28 lines
563 B
Ruby
=begin
|
|
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.
|
|
For example, in an arrya A:
|
|
A[]=[-7,1,5,2,-4,3,0]
|
|
3 is an equilibrium index, because:
|
|
A[0] + A[1] + A[2] = A[4] + A[5] + A[6]
|
|
Time-complexity: O(n)
|
|
Auxiliary-space: O(1)
|
|
=end
|
|
|
|
def find_equilibrium(a)
|
|
len = a.length
|
|
leftsum=0
|
|
rightsum=0
|
|
for x in a
|
|
rightsum+=x
|
|
end
|
|
for i in 0...len
|
|
rightsum-=a[i]
|
|
if (leftsum == rightsum)
|
|
return i
|
|
end
|
|
leftsum+=a[i]
|
|
end
|
|
|
|
return -1
|
|
|
|
end |