快速排序爲不穩定排序,比如序列爲 5 3 4 3 8 9 , 現在中樞元素5和3(第4個元素)交換就會把元素3的穩定性打亂,不穩定發生在中樞元素和a[j] 交換的時刻。時間複雜度O(n*log2n)
void QuickSort(int buf[], int begin, int end)
{
int left = begin;
int right = end;
int tmp = buf[left];
if (left >= right)
return;
while (left != right)
{
while (left < right && buf[right] >= tmp) right--;
if (buf[right] < tmp) buf[left] = buf[right];
while (left < right && buf[left] <= tmp) left++;
if (buf[left] > tmp) buf[right] = buf[left];
}
buf[left] = tmp;
QuickSort(buf, begin, left-1);
QuickSort(buf, left+1, end);
}