Algorithm: Sort the array placing negative numbers before positive numbers, and keep the orders.

Study the article about sorting the array by even/odd number, placing odd numbers before even number. And then, next question, sorting the array by negative/positive number, and keep the order.  - on May 4, 2015, 8;30pm - 11:00pm, read 2. 5 hours.

First question, 输入一个整数数组，调整数组中数字的顺序，使得所有奇数位于数组的前半部分，所有偶数位于数组的后半部分。要求时间复杂度为O(n)

https://github.com/jlycoding/The-Art-Of-Programming-By-July/blob/master/ebook/zh/02.06.md

http://www.cnblogs.com/legendmaner/archive/2013/04/22/3035050.html

http://www.cnblogs.com/legendmaner/archive/2013/04/04/2999769.html

http://www.careercup.com/question?id=5201559730257920

Read the paper: STABLE MINIMUM SPACE PARTITIONING IN LINEAR TIME Next question: 一个未排序整数数组，有正负数，重新排列使负数排在正数前面，并且要求不改变原来的正负数之间相对顺序，比如： input: 1,7,-5,9,-12,15 ans: -5,-12,1,7,9,15 要求时间复杂度O(n),空间O(1)