Sort Colors

Follow up:
A rather straight forward solution is a two-pass algorithm using counting sort.
First, iterate the array counting number of 0‘s, 1‘s, and 2‘s, then overwrite array with total number of 0‘s, then 1‘s and followed by 2‘s.

Could you come up with an one-pass algorithm using only constant space?

基本思路：

把红色往左边移，把蓝色往右边移动。

	public void swap(int[] A,int i,int j)
	{
		int tmp = A[i];
		A[i] = A[j];
		A[j] = tmp;
	}
	public void sortColors(int[] A)
	{
		if (A==null||A.length == 1)
			return ;
		int left = 0;
		int right = A.length-1;
		int current = 0;
		
		while(current<=right)//注意这里是小于等于，防止出现{1,0}的情况
		{
			if(A[current]==0)
			{
				swap(A, left, current);
				left++;
				if(current<left)//防止出现首个元素就是0的情况
					current = left;
			}
			else if(A[current]==2)
			{
				swap(A, right, current);
				right--;
			}
			else
				current++;
		}
	}