方法1：快速排序的partition思想

class Solution {
    public void sortColors(int[] nums) {
        int l = 0;
        int r = nums.length-1;
        int cur = l;
        while (cur <= r){
            if (nums[cur] == 0){
                swap(nums,cur++,l++);
            }else if (nums[cur] == 1){
                cur++;
            }else{
                swap(nums,cur,r--);
            }
        }
    }
    
    public void swap(int[] nums,int i,int j){
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }
}

方法2：计数排序

class Solution {
    public void sortColors(int[] nums) {
        int[] items = new int[3];
        for (int i = 0;i < nums.length;i ++){
            items[nums[i]]++;
        }
        
        int index = 0;
        for (int i = 0;i < items.length;i ++){
            for (int j = 0;j < items[i];j ++){
                nums[index++] = i;
            }
        }
    }
}