Given an array A, partition it into two (contiguous) subarrays left and
right so that:
left is less than or equal to every element in right.
left and right are non-empty.left has the smallest possible size.Return the length of left after such a partitioning. It
is guaranteed that such a partitioning exists.
Example 1:
Input: [5,0,3,8,6] Output: 3 Explanation: left = [5,0,3], right = [8,6]
Example 2:
Input: [1,1,1,0,6,12] Output: 4 Explanation: left = [1,1,1,0], right = [6,12]