归并排序-nlogn

//归并排序
void mergeArray(int a[], int first, int mid, int last, int temp[])        //对两个有序数列合并
{
int i = first;
int j = mid + 1;
int m = mid;
int n = last;
int k = 0;
//每次把两个数列中较小的值存在temp中
while(i <= m && j <= n)
{
if(a[i]<= a[j])
{
temp[k++] = a[i++];
}
else
{
temp[k++] = a[j++];
}
}
//哪一个数列先完成拷贝就把另一个数列的剩余的值存在temp中
while(i <= m)
{
temp[k++] = a[i++];
}
while(j <= n)
{
temp[k++] = a[j++];
}
//把temp中的值拷贝到a中
for(int 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 = (last + first)/2;   //注意用加号,不是减号,
//将数组划分成由单个数组成的数列,则就可看成是每个数列都是有序的,可以用mergeArray函数了
mergeSort(a, first, mid, temp);
mergeSort(a, mid+1, last, temp);
mergeArray(a, first, mid, last, temp);
}
}
bool MergeSort(int a[], int n)
{
int *p = new int
;
if(p == NULL)
{
return false;
}
else
{
mergeSort(a, 0, n-1, p);
delete[] p;
return true;
}
}