顺序排序法有哪些

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　　在计算器科学与数学中，一个排序算法（英语：Sorting algorithm）是一种能将一串数据依照特定排序方式进行排列的一种算法。本文将总结几类常用的排序算法，包括冒泡排序、选择排序、插入排序、快速排序和归并排序。

1、冒泡排序

原理图

理解：通过重复地遍历要排序的列表，比较每对相邻的项目，并在顺序错误的情况下交换它们。

代码：

public class BubbleSort {
  
    // logic to sort the elements
    public static void bubble_srt(int array[]) {        int n = array.length;        int k;        for (int m = n; m >= 0; m--) {            for (int i = 0; i < n - 1; i++) {
                k = i + 1;                if (array[i] > array[k]) {
                    swapNumbers(i, k, array);
                }
            }
            printNumbers(array);
        }
    }  
    private static void swapNumbers(int i, int j, int[] array) {  
        int temp;
        temp = array[i];        array[i] = array[j];        array[j] = temp;
    }  
    private static void printNumbers(int[] input) {          
        for (int i = 0; i < input.length; i++) {
            System.out.print(input[i] + ", ");
        }
        System.out.println("\n");
    }  
    public static void main(String[] args) {        int[] input = { 4, 2, 9, 6, 23, 12, 34, 0, 1 };
        bubble_srt(input);
    }
}

2、选择排序

原理图

理解：内部循环查找下一个最小（或最大）值，外部循环将该值放入其适当的位置。

代码：

public class SelectionSort { 
    public static int[] doSelectionSort(int[] arr){         
        for (int i = 0; i < arr.length - 1; i++)
        {            int index = i;            for (int j = i + 1; j < arr.length; j++)                if (arr[j] < arr[index]) 
                    index = j;      
            int smallerNumber = arr[index];  
            arr[index] = arr[i];
            arr[i] = smallerNumber;
        }        return arr;
    }     
    public static void main(String a[]){         
        int[] arr1 = {10,34,2,56,7,67,88,42};        int[] arr2 = doSelectionSort(arr1);        for(int i:arr2){
            System.out.print(i);
            System.out.print(", ");
        }
    }
}

3、插入排序

原理图

理解：每一步将一个待排序的记录，插入到前面已经排好序的有序序列中去，直到插完所有元素为止。

代码:

public class InsertionSort {
 
    public static void main(String a[]){        int[] arr1 = {10,34,2,56,7,67,88,42};        int[] arr2 = doInsertionSort(arr1);        for(int i:arr2){
            System.out.print(i);
            System.out.print(", ");
        }
    }
     
    public static int[] doInsertionSort(int[] input){         
        int temp;        for (int i = 1; i < input.length; i++) {            for(int j = i ; j > 0 ; j--){                if(input[j] < input[j-1]){
                    temp = input[j];                    input[j] = input[j-1];                    input[j-1] = temp;
                }
            }
        }        return input;
    }
}

4、快速排序

原理图

理解：将原问题分解为若干个规模更小，但结构与原问题相似的子问题，递归地解这些子问题，然后将这些子问题的解组合为原问题的解。

代码：

public class QuickSort {
     
    private int array[];    private int length; 
    public void sort(int[] inputArr) {         
        if (inputArr == null || inputArr.length == 0) {            return;
        }        this.array = inputArr;
        length = inputArr.length;
        quickSort(0, length - 1);
    } 
    private void quickSort(int lowerIndex, int higherIndex) {         
        int i = lowerIndex;        int j = higherIndex;        // calculate pivot number, I am taking pivot as middle index number
        int pivot = array[lowerIndex+(higherIndex-lowerIndex)/2];        // Divide into two arrays
        while (i <= j) {            /**
             * In each iteration, we will identify a number from left side which 
             * is greater then the pivot value, and also we will identify a number 
             * from right side which is less then the pivot value. Once the search 
             * is done, then we exchange both numbers.
             */
            while (array[i] < pivot) {
                i++;
            }            while (array[j] > pivot) {
                j--;
            }            if (i <= j) {
                exchangeNumbers(i, j);                //move index to next position on both sides
                i++;
                j--;
            }
        }        // call quickSort() method recursively
        if (lowerIndex < j)
            quickSort(lowerIndex, j);        if (i < higherIndex)
            quickSort(i, higherIndex);
    } 
    private void exchangeNumbers(int i, int j) {        int temp = array[i];        array[i] = array[j];        array[j] = temp;
    }     
    public static void main(String a[]){
         
        MyQuickSort sorter = new MyQuickSort();        int[] input = {24,2,45,20,56,75,2,56,99,53,12};
        sorter.sort(input);        for(int i:input){
            System.out.print(i);
            System.out.print(" ");
        }
    }
}

5、归并排序

原理图

理解：将待排序的数列分成若干个长度为1的子数列，然后将这些数列两两合并；得到若干个长度为2的有序数列，再将这些数列两两合并；得到若干个长度为4的有序数列，再将它们两两合并；直接合并成一个数列为止。

代码：

public class MergeSort {
     
    private int[] array;    private int[] tempMergArr;    private int length; 
    public static void main(String a[]){         
        int[] inputArr = {45,23,11,89,77,98,4,28,65,43};
        MyMergeSort mms = new MyMergeSort();
        mms.sort(inputArr);        for(int i:inputArr){
            System.out.print(i);
            System.out.print(" ");
        }
    }     
    public void sort(int inputArr[]) {        this.array = inputArr;        this.length = inputArr.length;        this.tempMergArr = new int[length];
        doMergeSort(0, length - 1);
    } 
    private void doMergeSort(int lowerIndex, int higherIndex) {         
        if (lowerIndex < higherIndex) {            int middle = lowerIndex + (higherIndex - lowerIndex) / 2;            // Below step sorts the left side of the array
            doMergeSort(lowerIndex, middle);            // Below step sorts the right side of the array
            doMergeSort(middle + 1, higherIndex);            // Now merge both sides
            mergeParts(lowerIndex, middle, higherIndex);
        }
    } 
    private void mergeParts(int lowerIndex, int middle, int higherIndex) { 
        for (int i = lowerIndex; i <= higherIndex; i++) {
            tempMergArr[i] = array[i];
        }        int i = lowerIndex;        int j = middle + 1;        int k = lowerIndex;        while (i <= middle && j <= higherIndex) {            if (tempMergArr[i] <= tempMergArr[j]) {                array[k] = tempMergArr[i];
                i++;
            } else {                array[k] = tempMergArr[j];
                j++;
            }
            k++;
        }        while (i <= middle) {            array[k] = tempMergArr[i];
            k++;
            i++;
        }
    }
}

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