输入n个整数，输出其中最小的k个

题目描述

输入n个整数，输出其中最小的k个。

输入描述

输入说明
1 输入两个整数
2 输入一个整数数组

输出描述

输出一个整数数组

输入例子

5 2
1 3 5 7 2

输出例子

1 2

算法实现

import java.util.Arrays;
import java.util.Scanner;

/*
* Declaration: All Rights Reserved !!!
*/
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
//        Scanner scanner = new Scanner(Main.class.getClassLoader().getResourceAsStream("data.txt"));
while (scanner.hasNext()) {
int n = scanner.nextInt();
int k = scanner.nextInt();
int[] arr = new int
;

for (int i = 0; i < n; i++) {
arr[i] = scanner.nextInt();
}

// 【1】方法一
System.out.print(getMinK(arr, k));

// 【2】方法二
//            Arrays.sort(arr);
//            StringBuilder builder = new StringBuilder();
//            for (int i = 0; i < k; i++) {
//                builder.append(arr[i]).append(' ');
//            }
//
//            System.out.print(builder.substring(0, builder.length() - 1));
}

scanner.close();
}

private static String getMinK(int[] arr, int k) {

if (k <= 0) {
return "";
} else if (k >= arr.length) {
StringBuilder b = new StringBuilder();
for (int i : arr) {
b.append(i).append(' ');
}

return b.toString();
} else {

int[] min = new int[k];

for (int i = 0; i < arr.length; i++) {
if (i < k - 1) {
min[i] = arr[i];
} else if (i == k - 1) {
min[i] = arr[i];

// 下面要建大堆了
for (int j = min.length / 2; j >= 0; j--) {
shiftDown(min, j, min.length);
}
} else {
if (min[0] > arr[i]) {
min[0] = arr[i];
shiftDown(min, 0, min.length);
}
}
}

Arrays.sort(min);

StringBuilder b = new StringBuilder();
for (int i : min) {
b.append(i).append(' ');
}
return b.substring(0, b.length() - 1);
}
}

private static void shiftDown(int[] a, int i, int n) {
int child;
int tmp;
for (tmp = a[i]; 2 * i + 1 < n; i = child) {
// 左孩子
child = 2 * i + 1;
// 找较大的子结点
if (child + 1 < n && a[child] < a[child + 1]) {
child++;
}

if (tmp < a[child]) {
a[i] = a[child];
} else {
break;
}
}

a[i] = tmp;
}
}