# Paste: codility sample test

Author: dolson factor Sun, 28 Feb 2010 05:02:44
Plain Text |
```USING: kernel sequences math locals ;

:: equi_loop ( ret lhs rhs ele idx -- ret lhs rhs ) ret lhs ele + dup rhs = [ nip idx swap ] when rhs ele - ;
: equi ( seq -- idx ) [ drop -1 0 ] [ sum ] [ [ equi_loop ] each-index ] tri 2drop ;```

## Annotation: ss

Author: ss java Mon, 14 Nov 2011 17:06:55
Plain Text |
```A zero-indexed array A consisting of N integers is given. An equilibrium index of this array is any integer P such that 0 ≤ P < N and the sum of elements of lower indices is equal to the sum of elements of higher indices, i.e.
A + A + ... + A[P−1] = A[P+1] + ... + A[N−2] + A[N−1].
Sum of zero elements is assumed to be equal to 0. This can happen if P = 0 or if P = N−1.
For example, consider the following array A consisting of N = 7 elements:
A = -7   A =  1   A = 5
A =  2   A = -4   A = 3
A =  0
P = 3 is an equilibrium index of this array, because A + A + A = A + A + A.
P = 6 is also an equilibrium index, because: A + A + A + A + A + A = 0 and there are no elements with indices greater than 6.
P = 7 is not an equilibrium index, because it does not fulfill the condition 0 ≤ P < N.
Write a function
class Solution { public int equi(int[] A); }
that, given a zero-indexed array A consisting of N integers, returns any of its equilibrium indices. The function should return −1 if no equilibrium index exists.
Assume that:
N is an integer within the range [0..10,000,000];
each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].
For example, given array A such that
A = -7   A =  1   A = 5
A =  2   A = -4   A = 3
A =  0
the function may return 3 or 6, as explained above.```