Consider the first sample test. The optimal solution is obtained if the first subarray contains the first element only, the second subarray spans the next three elements and the last subarray contains the last element only. The sums of these subarrays are 5, 9 and 1, correspondingly.
Consider the second sample test. In the optimal solution, the first subarray consists of the first two elements and the second subarray consists of the third element only. Note that the last element does not belong to any subarray in this solution.