算法与数据结构-04-排序算法

冒泡排序（大小相邻比较，交换）：

package sgq0321;

import java.util.Arrays;

public class BubbleSort {

    public static void main(String[] args) {
        BubbleSort bubbleSort = new BubbleSort();
        System.out.println(Arrays.toString(bubbleSort.bubble(new int[]{9, 3, 1})));
    }

    public int[] bubble(int[] arr) {
        for (int i = 0; i < arr.length - 1; i++) {
            boolean flag = true;
            for (int j = 0; j < arr.length - i - 1; j++) {
                if (arr[j] > arr[j + 1]) {
                    flag = false;
                    int temp = arr[j + 1];
                    arr[j + 1] = arr[j];
                    arr[j] = temp;
                }
            }
            if (flag) {
                return arr;
            }
        }
        return arr;
    }
}

选择排序（默认排头最小值，后续有更小值进行交换）：

package sgq0321;

import java.util.Arrays;

public class SelectSort {

    public static void main(String[] args) {
        SelectSort bubbleSort = new SelectSort();
        System.out.println(Arrays.toString(bubbleSort.select(new int[]{9, 3, 1})));
    }

    public int[] select(int[] arr) {
        for (int i = 0; i < arr.length - 1; i++) {
            int min = i;
            int minValue = arr[i];
            for (int j = i; j < arr.length; j++) {
                if (arr[j] < minValue) {
                    minValue = arr[j];
                    min = j;
                }
            }
            if (min == i) continue;
            arr[min] = arr[i];
            arr[i] = minValue;
        }
        return arr;
    }
}

插入排序（原数组分前后两段，前有序后无序，后依次取值插入前合适位置）：

package sgq0321;

import java.util.Arrays;

public class InsertSort {

    public static void main(String[] args) {
        InsertSort bubbleSort = new InsertSort();
        System.out.println(Arrays.toString(bubbleSort.insert(new int[]{5,9, 3, 1})));
    }

    public int[] insert(int[] arr) {

        for (int i = 1; i < arr.length; i++) {
            // index of the position to be inserted
            int insertIndex=i-1;
            // the value of the current index location
            int currentValue=arr[i];
            // if currentValue < the sequence has been shot
            while(insertIndex>=0 && currentValue<arr[insertIndex]){
                // 前面的值后移
                arr[insertIndex+1]=arr[insertIndex];
                insertIndex--;
            }
            arr[insertIndex+1]=currentValue;
        }
        return arr;
    }
}

 快速排序

package sgq0321;

import java.util.Arrays;

public class QuickSort {

    public static void main(String[] args) {
        QuickSort bubbleSort = new QuickSort();
        int[] ints = {8, 9, 1, 7, 2, 3, 5, 4, 6, 0};
        bubbleSort.quick(ints, 0, ints.length - 1);
        System.out.println(Arrays.toString(ints));
    }

    public void quick(int[] arr, int left, int right) {
        int l = left;
        int r = right;
        int pivot = arr[(l + r) / 2];

        while (l < r) {
            while (arr[l]<pivot){
                l++;
            }

            while (arr[r]>pivot){
                r--;
            }

            if(l>r){
                break;
            }

            int temp=arr[l];
            arr[l]=arr[r];
            arr[r]=temp;

            r--;
            l++;

        }

        if(left<r){
            quick(arr,left,r);
        }

        if(l<right){
            quick(arr,l,right);
        }


    }
}