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void mergesort(int *arr, int lo, int hi)
{
if (hi - lo < 2) return;
int mi = (lo + hi) / 2;
mergesort(arr, lo, mi);
mergesort(arr, mi, hi);
int templo = lo;
int la = mi - lo; int lb = hi - mi;
int *temp1 = new int[la];
int *temp2 = new int[lb];
for (int i = 0; i < la; i++)
{
temp1[i]=arr[i+lo];
}
for (int j = 0; j < lb; j++)
{
temp2[j] = arr[j + mi];
}
int *a=temp1, *b=temp2;
while (a < (temp1 + la) && b < (temp2 + lb))
{
if (*a > *b)
{
arr[lo++] = *b;
b++;
}
else
{
arr[lo++] = *a;
a++;
}
}
if (a < (temp1 + la))
{
for (int i = lo; i < hi; i++)
{
arr[lo++] = *(a++);
}
}
else if (b < (temp2 + lb))
{
for (int i = lo; i < hi; i++)
{
arr[lo++] = *(b++);
}
}
lo = templo;
delete[] temp1;
delete[] temp2;
}