分治-1-归并排序（Divide and Conquer-1-merge sort）

#include <stdio.h>
#define INFINITY 999999
#define LEN(A) ((sizeof (A)) / (sizeof A[0]))

void print_array(int A[], int len)
{
    int i;
    /*
    int len = LEN(A);
    sizeof on array function parameter will return size of 'int *' instead of 'int []'
      [-Wsizeof-array-argument]
        int len = LEN(A);
                  ^
    */
    for (i = 0; i < len; i++)
        printf("%d, ", A[i]);
    putchar('\n');
}
//merge将本次合并的两个array分别打印
void merge(int A[], int p, int q, int r)
{
    int k, i, j;
    int n1 = q - p + 1;
    int n2 = r - q;
    int L[n1+1], R[n2+1];

    for (i = 0; i < n1; i++)
        L[i] = A[p+i];
    L[n1] = INFINITY;
    print_array(L, n1+1);

    for (j = 0; j < n2; j++)
        R[j] = A[q+1+j];
    R[n2] = INFINITY;
    print_array(R, n2+1);

    i = j = 0;
    for (k = p; k <= r; k++) {
        if (L[i] <= R[j]) {
            A[k] = L[i];
            i++;
        } else {
            A[k] = R[j];
            j++;
        }
    }
}

void mergeSort(int A[], int p, int r)
{
    if (p < r) {
        int q = (p+r)/2;
        mergeSort(A, p, q);
        mergeSort(A, q+1, r);
        merge(A, p, q, r);
    }
}

int main(int argc, char *argv[])
{
    int A[] = {5, 6, 7, 8, 9, 10, 11, 12, 12, -3, 1, 2, 3, 4};
    merge(A, 0, 8, 13);
    print_array(A, LEN(A));

    int B[] = {2, 4, 5, 7, 1, 3, 2, 6};
    mergeSort(B, 0, LEN(B)-1);
    print_array(B, LEN(B));

    return 0;
}