Alternating subarray prefix

There's an array A consisting of N non-zero integers A1..N. A subarray of A is called alternating if any two adjacent elements in it have different signs (i.e. one of them should be negative and the other should be positive). For each x from 1 to N, compute the length of the longest alternating subarray that starts at x - that is, a subarray Ax..y for the maximum possible y ≥ x. The length of s