归并排序文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html
归并排序算法是采用分治法的一个非常典型的应用。归并排序的思想是将一个数组中的数都分成单个的；对于单独的一个数，它肯定是有序的，然后，我们将这些有序的单个数在合并起来，组成一个有序的数列。这就是归并排序的思想。它的时间复杂度为O(N*logN)。文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html
代码实现文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html
using namespace std;//将有二个有序数列a[first...mid]和a[mid...last]合并。
void mergearray(int a[], int first, int mid, int last, int temp[])
{
int i = first, j = mid + 1;
int m = mid, n = last;
int k = 0;文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html
while (i <= m && j <= n)
{
if (a[i] <= a[j])
temp[k++] = a[i++];
else
temp[k++] = a[j++];
}文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html
while (i <= m)
temp[k++] = a[i++];文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html
while (j <= n)
temp[k++] = a[j++];文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html
for (i = 0; i < k; i++)
a[first + i] = temp[i];
}
void mergesort(int a[], int first, int last, int temp[])
{
if (first < last)
{
int mid = (first + last) / 2;
mergesort(a, first, mid, temp); //左边有序
mergesort(a, mid + 1, last, temp); //右边有序
mergearray(a, first, mid, last, temp); //再将二个有序数列合并
}
}文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html
bool MergeSort(int a[], int n)
{
int *p = new int[n];
if (p == NULL)
return false;
mergesort(a, 0, n - 1, p);
delete[] p;
return true;
}文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html
int main()
{
int arr[] = {2, 1, 4};
MergeSort(arr, 3);文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html
for (int i = 0; i < 3; ++i)
{
cout<<arr[i]<<" ";
}
cout<<endl;
}文章源自菜鸟学院-https://www.cainiaoxueyuan.com/ymba/9464.html