Equilibrium index

func eq_index(nums) {
    var (i, sum, sums) = (0, 0, Hash.new);
    nums.each { |n|
        sums{2*sum + n} := [] -> append(i++)
        sum += n;
    }
    sums{sum} \\ [];
}

Test:

var indices = [
  [-7, 1, 5, 2,-4, 3, 0],
  [2, 4, 6],
  [2, 9, 2],
  [1,-1, 1,-1, 1,-1, 1],
]
 
indices.each { |x|
    say ("%s => %s" % @|[x, eq_index(x)].map{.dump});
}

Output:

[-7, 1, 5, 2, -4, 3, 0] => [3, 6]
[2, 4, 6] => []
[2, 9, 2] => [1]
[1, -1, 1, -1, 1, -1, 1] => [0, 1, 2, 3, 4, 5, 6]