选择使用ArrayList排序

Question

我正在尝试使用ArrayList对选择排序进行编码。我的程序要求我创建一个大小为20的数组，并用1到1000之间的随机整数填充它(没有用户输入或硬代码)。输出将需要显示原始的未排序整数列表，并在单独的一行上显示排序算法的每次通过。

我试着为选择排序创建一个方法，所以这就是我的困境，因为我不知道如何将代码实现到我的主方法中。

我希望我的输出如下所示(尽管当我尝试做20时，它只显示5个整数)：

未排序列表：3 68 298 290 1
通行证1:1 68 298 290 3
合格证2:1 3 298 290 68
通过证4:1 3 68 290 298

// Used to capture keyboard input
import java.util.*;
// Our class called SelectionSort
public class SelectionSort {
// Create doSelectionSort method 
public static int[] doSelectionSort(int[] arr) {
for (int i = 0; i < arr.length - 1; i++) {
int pos = i;
// find position of smallest num between (i + 1)th element and last element
for (int j = i + 1; j <= arr.length; j++) {
if (arr[j] < arr[pos])
pos = j;
// Swap min (smallest num) to current position on array
int min = arr[pos];
arr[pos] = arr[i];
arr[i] = min;
}
}
return arr;
}
// Main method
public static void main(String[] args) {
ArrayList<Integer> array = new ArrayList<Integer>(); // Declare and instantiate a new ArrayList object
Scanner userChoice = new Scanner(System.in); // User input for quitting program
String choice = ""; // Will hold user choice to quit program
boolean inputFlag = false; // True if input is valid, false otherwise
// Repeat program until user chooses to quit
while (inputFlag = true) {
System.out.print("nWould you like to continue the program? (Y/N): ");
choice = userChoice.nextLine();
if (choice.equalsIgnoreCase("Y")) {
try {
/* Create an array of size 20 and populate it with random integers between 1 and 1000.
Do not ask user for the numbers and do not hard code them */
for (int i = 0; i < 20; i++) {
int integer = (int)(1000.0 * Math.random());
array.add(integer);
}
System.out.print("nUNSORTED LIST: ");
//Display the 20 size of the unsorted ArrayList 
for (int i = 0; i < array.size() - 1; i++) {
System.out.print(array.get(i) + ", ");
}
// Shows very last integer with a period
System.out.print(array.get(array.size() - 1) + "."); 
System.out.println();
}
catch (IndexOutOfBoundsException e) {
System.out.println("nThere is an out of bounds error in the ArrayList.");
}
// Display each pass of the sorting algorithm on a separate line
for (int i = 1; i < array.size(); i++) {
System.out.print("PASS " + i + ": ");
for (int arr2:array) {
System.out.print(arr2 + ", ");
}
System.out.print(array.get(array.size() - 1) + ".n");
}
array.clear();
}
else if (choice.equalsIgnoreCase("N")) {
break;
}
// Error message when inputting anything other than Y/N
else { 
System.out.println("nERROR. Only Y, y, N, or n may be inputted.");
System.out.println("Please try again.");
}
}
}
}

我也很难从每次传球中删除最后一个数字，因为它显示了两次。。你知道我该怎么做吗？

很抱歉我的编码很糟糕，我还在努力理解它。

Answer 1

我修复了您的代码，现在应该可以工作了。

// Used to capture keyboard input
import java.util.*;
// Our class called SelectionSort
public class SelectionSort {
// Create doSelectionSort method 
public static void doSelectionSort(ArrayList<Integer> arr) {
for (int i = 0; i < arr.size(); i++) {
// find position of smallest num between (i + 1)th element and last element
int pos = i;
for (int j = i; j < arr.size(); j++) {
if (arr.get(j) < arr.get(pos))
pos = j;
}
// Swap min (smallest num) to current position on array
int min = arr.get(pos);
arr.set(pos, arr.get(i));
arr.set(i, min);
printOut(i + 1, arr);
}
}
private static void printOut(int pass, ArrayList<Integer> array) {
System.out.print("PASS " + pass + ": ");
for (int i = 0; i < array.size() - 1; i++) {
System.out.print(array.get(i) + ", ");
}
// Shows very last integer with a period
System.out.print(array.get(array.size() - 1) + "."); 
System.out.println();
}
// Main method
public static void main(String[] args) {
ArrayList<Integer> array = new ArrayList<Integer>(); // Declare and instantiate a new ArrayList object
Scanner userChoice = new Scanner(System.in); // User input for quitting program
String choice = ""; // Will hold user choice to quit program
boolean inputFlag = false; // True if input is valid, false otherwise
// Repeat program until user chooses to quit
while (inputFlag = true) {
System.out.print("nWould you like to continue the program? (Y/N): ");
choice = userChoice.nextLine();
if (choice.equalsIgnoreCase("Y")) {
try {
/* Create an array of size 20 and populate it with random integers between 1 and 1000.
Do not ask user for the numbers and do not hard code them */
for (int i = 0; i < 20; i++) {
int integer = (int)(1000.0 * Math.random());
array.add(integer);
}
System.out.print("nUNSORTED LIST: ");
//Display the 20 size of the unsorted ArrayList 
for (int i = 0; i < array.size() - 1; i++) {
System.out.print(array.get(i) + ", ");
}
// Shows very last integer with a period
System.out.print(array.get(array.size() - 1) + "."); 
System.out.println();
doSelectionSort(array);
}
catch (IndexOutOfBoundsException e) {
System.out.println("nThere is an out of bounds error in the ArrayList.");
}
}
else if (choice.equalsIgnoreCase("N")) {
break;
}
// Error message when inputting anything other than Y/N
else { 
System.out.println("nERROR. Only Y, y, N, or n may be inputted.");
System.out.println("Please try again.");
}
}
}
}

Answer 2

您的方法doSelectionSort看起来不错，但它完成了整个排序。如果你想显示每个迭代，你只需要添加一行：

public static int[] doSelectionSort(int[] arr) {
for (int i = 0; i < arr.length - 1; i++) {
int pos = i;
// find position of smallest num between (i + 1)th element and last element
for (int j = i + 1; j <= arr.length; j++) {
if (arr[j] < arr[pos])
pos = j;
// Swap min (smallest num) to current position on array
int min = arr[pos];
arr[pos] = arr[i];
arr[i] = min;
}
System.out.println("Pass "+pos+" : "+arr);
}
return arr;
}