75. Sort Colors

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.

题目要求一次过，使用两个指针，以及一个下标。注意的一点是0只会与1交换，所以可以进行index++

public class Solution {    public void sortColors(int[] nums) {        int p1 = 0, p2 = nums.length - 1, index = 0;    while (index <= p2) {        if (nums[index] == 0) {            nums[index] = nums[p1];            nums[p1] = 0;            p1++;        }        if (nums[index] == 2) {            nums[index] = nums[p2];            nums[p2] = 2;            p2--;            index--;        }        index++;    }    }}