title: how to merge two sorted integer array in place using O(n) time and O(1) space cost
body: <p>For example, given an integer array and its two consecutive sequence 's beginning position which are 'b1' and 'b2', furthermore provided with the position 'last' which indicates the second sequence's ending position. From array[b1] to array [b2-1] and from array [b2] to array[last] are both in order separately, how to merge them in place <strong>using O(n) time and  O(1) space</strong> cost?</p>