最小的K個數

import java.lang.*;
import java.util.ArrayList;
public  class Main {
    public static void main(String args[]) {
        int[] a = new int[]{1, 8, 4, 2};
        Solution solution = new Solution();
       System.out.println(solution.GetLeastNumbers_Solution(a, 3));
    }
}

class Solution {
    public ArrayList<Integer> GetLeastNumbers_Solution(int[] input, int k) {

        if(input==null || input.length==0 || k<0 || k>input.length)
            return new ArrayList<>();
//            Arrays.sort(input);
        //快排
        else {
            ArrayList<Integer> x = new ArrayList<>();
            int begin = 0;
            int end = input.length;
         while (k>begin) {
    for (int i = begin + 1; i < end; i++)
        if (input[begin] > input[i]) {
            int a = 0;
            a = input[i];
            input[i] = input[begin];
            input[begin] = a;
        }
    begin++;
}
for (int i = 0; i < k; i++) {
                x.add(input[i]);
            }
            return x;

        }
    }
}