Merge Sort

#include <limits.h>
void merge(int* a,int la,int lb);

void mergeSort(int* p,int l)
{
    if(l<=1)
        return;
    int q = l>>1;
    mergeSort(p,q);
    mergeSort(p+q,l-q);
    merge(p,q,l-q);
}

void merge(int* a,int la,int lb)
{
    int* a1 = new int[la+1];
    int* b1 = new int[lb+1];
    for(int i = 0;i<la;++i)
        a1[i] = a[i];
    int* b = a+la;
    for(int i = 0;i<lb;++i)
        b1[i] = b[i];
    a1[la] = INT_MAX;
    b1[lb] = INT_MAX;
    int p = 0, q = 0;
    for(int i = 0;i<la+lb;++i)
        if(a1[p]<=b1[q])
            a[i] = a1[p++];
        else
            a[i] = b1[q++];
    delete a1;
    delete b1;
}