import java.util.Arrays;

public class Algorithm {

    public static void main(String[] args) {

        int[] nums = {1,0,2,2,1,0,2,0,2,0,0,2,1,1};
        new Solution().sortColors(nums);

        System.out.println(Arrays.toString(nums));
    }
}

class Solution {
    public void sortColors(int[] nums) {

        if (nums == null || nums.length == 0) {
            return;
        }

        /**
         * 三路快速排序法的思路
         * 迴圈不變數：arr[0, lt] == 0，arr[lt + 1, i] == 1，arr[gt, nums.length - 1] == 2
         */
        int lt = -1;
        int gt = nums.length;
        int i = lt + 1;

        while (i < gt) {

            if (nums[i] == 0){

                lt++;
                swap(nums, lt, i);
                i++;
            } else if (nums[i] == 1){
                i++;
            }else {
                gt--;
                swap(nums, gt, i);
            }
        }
    }

    public void swap(int[] arr, int i, int j){

        int temp;

        temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}
 

https://leetcode-cn.com/problems/sort-colors/