Give an array which has n integers,it has both positive and negative integers.Now you need sort this array in a special way.After that,the negative integers should in the front,and the positive integers should in the back.Also the relative position should not be changed.

eg. -1 1 3 -2 2 ans: -1 -2 1 3 2.

O(n)time complexity and O(1) space complexity is required .