归并排序的代码实现（递归与非递归）

#include <iostream>

using namespace std;

//----------------------------------------------------------
// 归并排序（递归实现）

// 将有二个有序数列data[first...mid]和data[mid...last]合并
void Merge(int data[], int first, int mid, int last, int temp[])
{
    int i = first, j = mid + 1;
    int m = mid,   n = last;
    int k = 0;

    while (i <= m && j <= n)
    {
        if (data[i] <= data[j])
            temp[k++] = data[i++];
        else
            temp[k++] = data[j++];
    }

    while (i <= m)
        temp[k++] = data[i++];

    while (j <= n)
        temp[k++] = data[j++];

    for (i = 0; i < k; i++)
        data[first + i] = temp[i];
}

void RecursiveMergeSort(int data[], int first, int last, int temp[])
{
    if (first < last)
    {
        int mid = (first + last) / 2;
        RecursiveMergeSort(data, first, mid, temp);    // 左边有序
        RecursiveMergeSort(data, mid + 1, last, temp); // 右边有序
        Merge(data, first, mid, last, temp);           // 再将二个有序数列合并
    }
}

bool MergeSort(int data[], int count)
{
    int * buffer = new int[count];
    if (buffer == NULL)
        return false;

    RecursiveMergeSort(data, 0, count - 1, buffer);

    delete[] buffer;
    return true;
}

//----------------------------------------------------------
// 归并排序（非递归实现）

// 将data[]中相邻长度为step的子序列两两归并到temp[]
void MergePass(int data[],int temp[],int step, int count)
{
    int i = 0;

    while(i < count - 2*step)
    {
        Merge(data, i, i + step - 1, i + 2*step - 1, temp); // 两两归并
        i = i + 2*step;
    }

    if(i < count - step) // 归并最后两个序列
        Merge(data, i, i + step - 1, count - 1, temp);
}

bool MergeSort2(int data[], int count)
{
    int * buffer = new int[count];
    if (buffer == NULL)
        return false;

    int step = 1;
    while(step < count)
    {
        MergePass(data, buffer, step, count);
         step *= 2; // 子序列长度加倍
    }

    delete[] buffer;
    return true;
}

int main()
{
    int array[] = {9, 6, 3, 8, 7, 1, 5, 2, 4};
    int count = sizeof(array) / sizeof(array[0]);

    // MergeSort(array, count);
    MergeSort2(array, count);

    for(int i = 0; i < count; ++i)
        cout << array[i] << " ";

    cout << endl;

    return 0;
}