main函数

int main(void) {
  int n;
  scanf("%d", &n);
  if (n <= 0) {
    puts("");
  }
  vector<int> vec(n);
  for (int i = 0; i < n; ++i) {
    scanf("%d", &vec[i]);
  }
  quickSort(&vec[0], 0, n - 1);
  for (int i = 0; i < n; ++i) {
    printf("%d ", vec[i]);
  }
  puts("");
  return 0;
}

左右指针不取右，j和j+1

void quickSort(int* arr, int left, int right) {
  if (left >= right) {
    return;
  }
  int pivot = arr[left + ((right - left) >> 1)];
  int i = left - 1;
  int j = right + 1;
  while (i < j) {
    while (arr[++i] < pivot) {
    }
    while (arr[--j] > pivot) {
    }
    if (i < j) {
      swap(arr[i], arr[j]);
    }
  }
  quickSort(arr, left, j);
  quickSort(arr, j + 1, right);
}

左右指针不取左，i-1和i

void quickSort(int* arr, int left, int right) {
  if (left >= right) {
    return;
  }
  int pivot = arr[(static_cast<int64_t>(left) + right + 1) >> 1];
  int i = left - 1;
  int j = right + 1;
  while (i < j) {
    while (arr[++i] < pivot) {
    }
    while (arr[--j] > pivot) {
    }
    if (i < j) {
      swap(arr[i], arr[j]);
    }
  }
  quickSort(arr, left, i - 1);
  quickSort(arr, i, right);
}

快慢指针法，取左

void quickSort(int* arr, int left, int right) {
  if (left >= right) {
    return;
  }
  int pivot = arr[left];
  int i = left;
  int j = left + 1;
  while (j <= right) {
    if (arr[j] < pivot) {
      ++i;
      swap(arr[i], arr[j]);
    }
    ++j;
  }
  swap(arr[i], arr[left]);
  quickSort(arr, left, i - 1);
  quickSort(arr, i + 1, right);
}

快慢指针法，取右

void quickSort(int* arr, int left, int right) {
  if (left >= right) {
    return;
  }
  int pivot = arr[right];
  int i = left - 1;
  int j = left;
  while (j < right) {
    if (arr[j] < pivot) {
      ++i;
      swap(arr[i], arr[j]);
    }
    ++j;
  }
  ++i;
  swap(arr[i], arr[right]);
  quickSort(arr, left, i - 1);
  quickSort(arr, i + 1, right);
}