归并排序(非递归实现)

Posted 2021-02-20 laydown

import java.util.Arrays;

/**
 * 归并排序(非递归实现)
 */
public class MergeSort2 {

    public static void main(String[] args) {
        // 测试次数
        int times = 50000;

        int maxNum = 100;
        int maxSize = 100;
        for (int i = 0; i < times; i++) {
            // 生成随机数组
            int[] arr1 = generateArray(maxNum, maxSize);
            // 复制
            int[] arr2 = copyArray(arr1);
            // 归并排序
            mergeSort(arr1);
            // Api排序
            Arrays.sort(arr2);
            // 比较排序结果
            if (!arrayEquals(arr1, arr2)) {
                System.out.println("Sort failed!!! at " + i);
                System.out.println(Arrays.toString(arr1));
                System.out.println(Arrays.toString(arr2));
                return;
            }
        }
        System.out.println("Sort success");
    }

    public static void mergeSort(int[] arr) {
        if (arr == null || arr.length < 2) {
            return;
        }
        int mergeSize = 1;
        int size = arr.length;
        while (mergeSize < size) {
            int l = 0;
            while (l < size) {
                int mid = l + mergeSize - 1;
                if (mid >= size) {
                    break;
                }
                int r = Math.min(mid + mergeSize, size - 1);
                merge(arr, l, mid, r);
                l = r + 1;
            }
            if (mergeSize > (size >> 1)) {
                break;
            }
            mergeSize <<= 1;
        }
    }

    public static void merge(int[] arr, int left, int mid, int right) {
        int[] help = new int[right - left + 1];
        int index = 0;
        int po1 = left;
        int po2 = mid + 1;
        while (po1 <= mid && po2 <= right) {
            help[index++] = arr[po1] < arr[po2] ? arr[po1++] : arr[po2++];
        }
        while (po1 <= mid) {
            help[index++] = arr[po1++];
        }
        while (po2 <= right) {
            help[index++] = arr[po2++];
        }
        for (int i = 0; i < help.length; i++) {
            arr[left + i] = help[i];
        }
    }

    /**
     * 生成随机数组
     *
     * @param maxNum  最大数
     * @param maxSize 数组最大大小
     * @return 随机数组
     */
    private static int[] generateArray(int maxNum, int maxSize) {
        int[] arr = new int[(int) (maxSize * Math.random())];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = (int) (maxNum * Math.random()) - (int) (maxNum * Math.random());
        }
        return arr;
    }

    /**
     * 复制数组
     *
     * @param arr 要复制的数组
     * @return 复制的数组
     */
    private static int[] copyArray(int[] arr) {
        if (arr == null) {
            return null;
        }
        int[] copy = new int[arr.length];
        for (int i = 0; i < arr.length; i++) {
            copy[i] = arr[i];
        }
        return copy;
    }

    /**
     * 判断两数组是否完全相同
     *
     * @param arr1 数组1
     * @param arr2 数组2
     * @return 是否相同
     */
    private static boolean arrayEquals(int[] arr1, int[] arr2) {
        if (arr1 == arr2) {
            return true;
        }
        if (arr1 == null || arr2 == null || arr1.length != arr2.length) {
            return false;
        }
        for (int i = 0; i < arr1.length; i++) {
            if (arr1[i] != arr2[i]) {
                return false;
            }
        }
        return true;
    }

}

/* 如有错误，欢迎批评指正 */