Java 插入排序中的错误

Question

I've attempted to code an Insertion Sort in java via pseudo code from a book. The output for this code should be numbers in ascending order but for some reason I get 10,4,5,6,7,8,9. Any help is greatly appreciated! Thanks!

public class InsertionSort {

    public int Array[] = {10,9,8,7,6,5,4};

    public static void main(String[] args) {
        InsertionSort obj1 = new InsertionSort();
    }

    public InsertionSort() {
        InsertionSortMethod();
        PrintArray();
    }

    public void InsertionSortMethod() {
        for(int j = 2; j < Array.length; j++) {
            int key = Array[j];
            int i = j - 1;
            while(i > 0 && Array[i] > key) {
                Array[i + 1] = Array[i];
                i = i - 1;
            }
            Array[i + 1] = key;
        }   
    }

    public void PrintArray() {
        for(int i = 0; i < Array.length; i++) {
            System.out.println(Array[i]);
        }
    }
}

Answer 1

Start the for loop from j=1 like this :

for(int j = 1; j < array.length; j++) {

and modify while loop condition like this:

while(i >= 0 && array[i] > key) {

Correct working code :

public class InsertionSort {

public int array[] = {10,9,8,7,6,5,4};

public static void main(String[] args) {
    InsertionSort obj = new InsertionSort();
    obj.insertionSortMethod();
    obj.printArray();
}


public void insertionSortMethod() {
    for(int j = 1; j < array.length; j++) {
        int key = array[j];
        int i = j - 1;
        while(i >= 0 && array[i] > key) {
            array[i + 1] = array[i];
            i = i - 1;
    }
        array[i + 1] = key;

    }   
}

public void printArray() {
    for(int i = 0; i < array.length; i++) {
        System.out.print(array[i] + " ");
    }
}

}

Answer 2

At the third line of your code ie,

InsertionSort obj1 = new InsertionSort();

You are making an object of InsertionSort class but in your code, it is defined as a function I think it is a constructor you must mention the class for more convenience of the reader.

Apart from that, you are starting your loop with 2 for(int j = 2; j < Array.length; j++) why so? your one element got missed so start j with 1 :)

Answer 3

Thanks to all the answers. I have also found by tracing the algorithm that flipping the second 'greater than' sign to a 'less than' sign on the 5th line of the algorithm does the trick for working in descending order. This may possibly be a typo in the book i'm reading. Thanks again!

Answer 4

try this method

 public int[] insertionSort(int[] list) {
            int i, j, key, temp;
            for (i = 1; i < list.length; i++) {
                key = list[i];
                j = i - 1;
                while (j >= 0 && key < list[j]) {
                    temp = list[j];
                    list[j] = list[j + 1];
                    list[j + 1] = temp;
                    j--;
                }

            }
            return list;
        }

Answer 5

package com.borntoinnovation.datastructure;

import java.util.Arrays;

public class SortingInsertion {

    public static void main(String[] args) {
        int[] array = new int[] { 4, 3, 2, 20, 12, 1, 5, 6 };

        for (int i = 0; i < array.length; i++) {
            for (int j = 0; j < i; j++) {
                if (array[i] < array[j]) {
                    int temp = array[i];
                    for (int k = i; k > j; k--) {
                        array[k] = array[k - 1];
                    }
                    array[j] = temp;
                }
            }
            System.out.println(Arrays.toString(array));
        }

    }// end of main()
}