/*************************************************************************
	> File Name: two-way-merge-sort.c
	> Description: two-way-merge-sort.c
	> Author: lkong
	> Mail: lkong@tencent.com 
	> Created Time: 2021-12-15 21:33:35
 ************************************************************************/

#include <stdio.h>
#include <stdlib.h>

// https://www.cnblogs.com/horizonice/p/4102553.html
// https://blog.csdn.net/darkrabbit/article/details/90240709

void Merge(int array[], int p, int q, int r);
void MergeSort(int array[], int p, int q);

int main()
{
    //int array[7] = {1,3,5,2,4,5,10};
    int array[8] = {5,2,4,7,1,3,2,6};
    int i = 0;

    MergeSort(array, 0, 7);
    //Merge(array, 0, 2, 6);

    for(i; i < 8; i++)
        printf("%d  ", array[i]);
    return 0;
}

//合并过程中 p<=q<r
void Merge(int array[], int p, int q, int r)
{
    int n1 = q - p + 1;
    int n2 = r - q;

    int *L;
    L = (int*)malloc(sizeof(int)*n1);
    int *R;
    R = (int*)malloc(sizeof(int)*n2);

    int i = 0;
    int j = 0;

    for(i; i < n1; i++)
        L[i] = array[i + p];
    for(j; j < n2; j++)
        R[j] = array[j + q  +1];

    i = j = 0;

    int k = p;

    while(i!=n1 && j!= n2)
    {
        if(L[i] <= R[j])
            array[k++] = L[i++];
        else
            array[k++] = R[j++];
    }

    while(i < n1)
        array[k++] = L[i++];
    while(j < n2)
        array[k++] = R[j++];

    free(L);
    free(R);
}

void MergeSort(int array[], int p, int q)
{
    if(p < q)
    {
        int r = (p+q)/2;
        MergeSort(array, p, r);
        MergeSort(array, r+1, q);
        Merge(array,p, r, q);
    }
}