Algorithm | 排序算法之归并排序

最新推荐文章于 2024-08-19 10:34:53 发布

原创最新推荐文章于 2024-08-19 10:34:53 发布 · 1.8k 阅读

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#排序算法

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本文深入讲解了多种排序算法，包括冒泡排序、快速排序、直接插入排序、希尔排序、直接选择排序、堆排序和归并排序。重点介绍了归并排序的实现原理、代码实现、时间与空间复杂度以及算法稳定性。

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基本思想

基本思想：分治法，合并

代码实现

实现1：

public static void mergeSort(int[] array, int first, int last) {
    if (first >= last) {
        return;
    }

    int middle = (first + last) / 2;
    mergeSort(array, first, middle);
    mergeSort(array, middle + 1, last);
    mergeArray(array, first, middle, last);
}

private static void mergeArray(int[] array, int first, int middle, int last) {
    int[] buffer = new int[last - first + 1];
    int i = first, j = middle + 1, k = 0;

    while (i <= middle && j <= last) {
        if (array[i] < array[j]) {
            buffer[k++] = array[i++];
        } else {
            buffer[k++] = array[j++];
        }
    }

    while (i <= middle) {
        buffer[k++] = array[i++];
    }

    while (j <= last) {
        buffer[k++] = array[j++];
    }

    for (i = 0; i < k; i++) {
        array[first + i] = buffer[i];
    }
}

实现2：共用一个缓存数组

public static void mergeSort(int[] array) {
    mergeSort(array, 0, array.length - 1, new int[array.length]);
}

private static void mergeSort(int[] array, int first, int last, int[] buffer) {
    if (first >= last) {
        return;
    }

    int middle = (first + last) / 2;
    mergeSort(array, first, middle, buffer);
    mergeSort(array, middle + 1, last, buffer);
    mergeArray(array, first, middle, last, buffer);
}

private static void mergeArray(int[] array, int first, int middle, int last, int[] buffer) {
    int i = first, j = middle + 1, k = 0;

    while (i <= middle && j <= last) {
        if (array[i] < array[j]) {
            buffer[k++] = array[i++];
        } else {
            buffer[k++] = array[j++];
        }
    }

    while (i <= middle) {
        buffer[k++] = array[i++];
    }

    while (j <= last) {
        buffer[k++] = array[j++];
    }

    for (i = 0; i < k; i++) {
        array[first + i] = buffer[i];
    }
}