Common sorting algorithms (7 types)

(3 messages) Interview high-frequency test points -- common sorting algorithms (7 types)_Scintillator. /'s Blog-CSDN Blog_Sorting Algorithm Interview

import java.util.Arrays;

/**
 * @program: complex
 * @description:
 * @author: DRY
 * @create: 2022-08-02 14:41
 **/
public class MySort {
    /**
     * 插入排序  稳定  O(n)
     * @param arr
     */
    public static void insertSort(int[] arr) {
        for (int i = 1; i < arr.length; i++) {
            int tmp = arr[i];
            int j = i - 1;
            for (;  j >= 0 ; j--) {
                if(arr[j] > tmp) {
                    arr[j + 1] = arr[j];
                } else{
                    break;
                }
            }
            arr[j + 1] = tmp;
        }
    }

    /**
     * 希尔排序  不稳定 O^1.3 ~ 1.5
     * @param arr
     */
    public static void shellSort(int[] arr) {
        int gap = arr.length;
        while(gap > 1) {
            shell(arr, gap);
            gap /= 2;
        }
        shell(arr,1);
    }

    private static void shell(int[] arr, int gap) {
        for (int i = 1; i < arr.length; i++) {
            int tmp = arr[i];
            int j = i - gap;
            for(; j >= 0; j -= gap) {
                if(arr[j] > tmp) {
                    arr[j + gap] = arr[j];
                } else{
                    break;
                }
            }
            arr[j + gap] = tmp;
        }
    }

    /**
     * 选择排序 不稳定  O(n^2)
     * @param arr
     */
    public static void selectSort(int[] arr) {
        for (int i = 0; i < arr.length; i++) {
            for (int j = i + 1; j < arr.length; j++) {
                if(arr[j] < arr[i]) {
                    swap(arr,i,j);
                }
            }
        }
    }

    /**
     * 堆排序  不稳定O(NlogN)
     * @param arr
     */
    public static void heapSort(int[] arr) {
        createHeap(arr);//将数组变为大根堆
        int end = arr.length - 1;
        while(end > 0) {
            swap(arr,0,end);
            shiftDown(arr,0,end);
            end--;
        }
    }

    private static void createHeap(int[] arr) {
        for (int parent = (arr.length - 1 - 1) / 2; parent >= 0 ; parent--) {
            shiftDown(arr,parent,arr.length);
        }
    }

    private static void shiftDown(int[] arr, int parent, int length) {
        int child = 2 * parent + 1;
        while( child < length) {
            if(child + 1 < length && arr[child] < arr[child + 1]) {
                child = child + 1;
            }
            if(arr[child] > arr[parent]) {
                swap(arr,child,parent);
                parent = child;
                child = 2 * parent + 1;
            } else {
                break;
            }
        }
    }

    /**
     * 冒泡排序 稳定 O(n^2)
     * @param arr
     */
    public  static void bubbleSort(int[] arr) {
        for (int i = 0; i < arr.length - 1; i++) {
            boolean flag = false;
            for (int j = 0; j < arr.length - i - 1; j++) {
                if(arr[j] > arr[j + 1]) {
                    swap(arr,j + 1,j);
                    flag = true;
                }
            }
            if(flag == false) {
                break;
            }
        }
    }

    /**
     * 快速排序 不稳定 O(NlogN)
     * @param arr
     */
    public static void quickSort(int[] arr) {
        quick(arr,0,arr.length - 1);
    }

    private static void quick(int[] arr, int left, int right) {
        if(left > right) {
            return;
        }
        int pivot = partition(arr,left, right);  //找到基准值
        quick(arr,left, pivot - 1);
        quick(arr,pivot + 1,right);
    }

    private static int partition(int[] arr, int left, int right) {
        int tmp = arr[left];
        while(left < right) {
            while(left < right && arr[right] >= tmp) {
                right--;
            }
            arr[left] = arr[right];
            while(left < right && arr[left] <= tmp) {
                left++;
            }
            arr[right] = arr[left];
        }
        arr[left] = tmp;
        return left;
    }


    /**
     * 归并排序 稳定 O(NlogN）
     * @param arr
     */
    public static void mergeSort(int[] arr) {
        mergeSortInternal(arr,0,arr.length - 1);
    }

    private static void mergeSortInternal(int[] arr, int low, int high) {
        if(low >= high) {
            return;
        }
        int mid = low + ((high - low) >>> 1);
        mergeSortInternal(arr, low, mid);
        mergeSortInternal(arr,mid +1, high);
        merge(arr,low,mid,high);
    }

    private static void merge(int[] arr, int low, int mid, int high) {
        int[] tmp = new int[high - low + 1];
        int k = 0;
        int s1 = low;
        int e1 = mid;
        int s2 = mid + 1;
        int e2 = high;
        while(s1 <= e1 && s2 <= e2) {
            if(arr[s1] <= arr[s2]) {
                tmp[k++] = arr[s1++];
            } else {
                tmp[k++] = arr[s2++];
            }
        }
        while(s1 <= e1) {
            tmp[k++] = arr[s1++];
        }
        while(s2 <= e2) {
            tmp[k++] = arr[s2++];
        }
        for (int i = 0; i < k; i++) {
            arr[i + low] = tmp[i];
        }
    }

    private static void swap(int[] arr, int i, int j) {
        int tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
    }

    public static void main(String[] args) {
        MySort mySort = new MySort();
        int[] data = {2,1,4,6,3,9,8,5,7};
        mySort.mergeSort(data);
        System.out.println(Arrays.toString(data));
    }
}