#include <iostream>
#include <assert.h>
using namespace std;


void myMerge(int a[], int from, int mid, int to)
{
    assert(from <= mid && mid < to);
    int* arr = new int[to-from+1];
    assert(arr);
    int i = from;
    int j = mid + 1;
    int index = 0;
    while(i <= mid && j <= to)
        arr[index++] = (a[i] < a[j] ? a[i++] : a[j++]);
    /*
    while(i <= mid && j <= to)
    {
        if(a[i] < a[j])    //指令流水，通常这个分支难以预测
            arr[index++] = a[i++];
        else
            arr[index++] = a[j++];
    }
    */
    while(i <= mid)
        arr[index++] = a[i++];
    while(j <= to)
        arr[index++] = a[j++];
    for(int k=0; k < index; ++k)
        a[from++] = arr[k];
    delete[] arr;
    arr = NULL;
}

void mergeSort(int a[], int from, int to)
{
    if(from < to)
    {
        int middle = ((to - from) >> 1) + from;
        mergeSort(a,from,middle);
        mergeSort(a,middle+1,to);
        myMerge(a,from,middle,to);
    }
}

template <typename T, size_t num>
void output(T  (&a)[num])
{
    for(size_t t=0; t<num; ++t)
        cout << a[t] << " ";
    cout << endl;
}

int main()
{
    const int len = 250000;
    int a[len];
    for(int i=0; i<len/2; ++i)
        a[i] = i;
    for(int i=len/2; i<len; ++i)
        a[i] = len - i;
    output(a);
    mergeSort(a,0,len-1);
    output(a);
    return 0;
}