Hoare partition

gistfile1.cpp

int Partition(int *a, int l, int r) {
  int x = a[l], i = l - 1, j = r;
  while (1) {
    do  j--; while (a[j] > x);
    do  i++; while (a[i] < x);
    if  (i < j)
      swap(a[i],a[j]);
    else
      return j + 1;
  }
}