leetcode------Sort Colors

标题：	Sort Colors
通过率：	32.5%
难度：	中等

Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue.

Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.

Note:
You are not suppose to use the library's sort function for this problem.

click to show follow up.

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?

本题就是排序的缩小版，数组中只会出现0，1，2三个数那么用三个指针去控制这个数

如果p[i]=0那么要把前面的1，2都往后移动一位，

如果p[i]=1那么要把前面的2移动一位

如果p[i]=2只用将2的指针更新

代码如下；

public class Solution {
    public void sortColors(int[] A) {
        int i=-1,j=-1,k=-1;
        for(int p=0;p<A.length;p++){
            if(A[p]==0){
                A[++k]=2;
                A[++j]=1;
                A[++i]=0;
            }
            else if(A[p]==1){
                A[++k]=2;
                A[++j]=1;
            }
            else if(A[p]==2){
                A[++k]=2;
            }
        }
    }
}