我有两种排序方法:插入排序和shell排序。其中两个工作函数我已经适应了来自普通C的C ++。问题是ins_sort函数工作得很好而shell_sort失败了。可能是什么原因?
bool less(QVector<int> &arr, int a, int b)
{
return arr[a] < arr[b];
}
// Performs swap on elements at a and b in QVector<int> arr
void qswap(QVector<int> &arr, int a, int b)
{
int temp = arr[a];
arr[a] = arr[b];
arr[b] = temp;
}
/* Failure is thrown in this method */
void shell_sort(GraphicsView &window, SwapManager &manager)
{
auto list = window.items();
QVector<int> arr;
for (auto item : list)
arr.push_back(static_cast<QGraphicsRectWidget*>(item)->m_number);
int N = arr.size();
int h = 1;
while (h < N/3) h = 3*h + 1;
while (h >= 1)
{
for (int i = h; i < N; ++i)
{
for (int j = i; less(arr, j, j-h) && j >= h; j -= h)
{
qswap(arr, j, j-h);
manager.addPair(j, j - h);
}
}
h /= 3;
}
}
那个人做得很好。
/* This method works just fine */
void ins_sort(GraphicsView &window, SwapManager &manager)
{
auto list = window.items();
int i, j;
QVector<int> arr;
for (auto item : list)
{
arr.push_back(static_cast<QGraphicsRectWidget*>(item)->m_number);
}
int N = arr.size();
for (i = 1; i < N; ++i)
{
for (j = i - 1; j != -1 && less(arr, j + 1, j); --j)
{
qswap(arr, j, j + 1);
manager.addPair(j, j + 1);
}
}
}
调试器指向&#34; qvector.h&#34;
中的这段代码 Q_ASSERT_X(i >= 0 && i < d->size, "QVector<T>::operator[]", "index out of range");
return data()[i]; }
答案 0 :(得分:1)
在for循环条件中,有必要检查j值之前比较项目:
for (int j = i; j >= h && less(arr, j, j-h); j -= h)