排序的第一天

归并排序与希尔排序

希尔排序

package com.m.suan_pai;


import java.util.Arrays;

public class Test {
    public static void main(String[] args) {
        int[] arr = {65, 45, 76, 546, 4, 5, 72, 36, 45, 72, 346, 52};
        xier(arr);
        System.out.println(Arrays.toString(arr));
        //[4, 5, 36, 45, 45, 52, 65, 72, 72, 76, 346, 546]
    }

    public static void xier(int[] arr) {
        //1.定义跨度
        int k = 1;
        while (k < arr.length) {
            k = k * 2 + 1;
        }

        do {
            k /= 2;
            for (int i = k; i < arr.length; i++) {
                int temp = arr[i];
                int j = i - k;
                while (j >= 0 && arr[j] > temp) {
                    arr[j + k] = arr[j];
                    j -= k;
                }
                arr[j + k] = temp;
            }
        } while (k > 1);

    }

}

归并排序

package com.m.suan_pai;


import java.util.Arrays;

public class Test {
    public static void main(String[] args) {
        int[] arr = {65, 45, 76, 546, 4, 5, 72, 36, 45, 72, 346, 52};
        sort(arr);
        System.out.println(Arrays.toString(arr));
        //[546, 346, 76, 72, 72, 65, 52, 45, 45, 36, 5, 4]
    }

    public static void sort(int[] arr) {
        int[] temp = new int[arr.length];
        sort(arr, 0, arr.length - 1, temp);
    }

    public static void sort(int[] arr, int left, int right, int[] temp) {
        if (left < right) {
            int mid = (left + right) / 2;
            //左分
            sort(arr, 0, mid, temp);
            //右分
            sort(arr, mid + 1, right, temp);
            //合并
            hebing(arr, left, mid, right, temp);
        }

    }


    public static void hebing(int[] arr, int left, int mid, int right, int[] temp) {
        //临时数组指针
        int index = 0;
        //左指针
        int i = left;
        //右指针
        int j = mid + 1;

        while (i <= mid && j <= right) {
            if (arr[j] > arr[i]) {
                temp[index++] = arr[j++];
            } else {
                temp[index++] = arr[i++];
            }
        }

        while (i <= mid) {
            temp[index++] = arr[i++];
        }

        while (j <= right) {
            temp[index++] = arr[j++];
        }

        index = 0;

        while (left <= right) {
            arr[left++] = temp[index++];
        }
    }
}

希尔排序核心代码，易错点

        
        int i = left;

        int j = mid + 1;

        int index = 0;

        while (i <= mid && j <= right) {
            if (arr[j] > arr[i]) {
                temp[index++] = arr[j++];
            } else {
                temp[index++] = arr[i++];
            }
        }