剑指offer面试题36：数组中的逆序对

#include "iostream"
using namespace std;
int InversePairsCore(int* data,int* copy,int start,int end)
{
if (start==end)
{
copy[start] = data[start];
return 0;
}
int length = (end - start) / 2;
int left = InversePairsCore(copy, data, start, start + length);
int right = InversePairsCore(copy, data, start + length + 1, end);
int i = start + length;
int j = end;
int indexCopy = end;
int count = 0;
while (i>=start&&j>=start+length+1)
{
if (data[i]>data[j])
{
copy[indexCopy--] = data[i--];
count += j - start - length;
}
else
{
copy[indexCopy--] = data[j--];
}
}
for (; i >= start; --i)
copy[indexCopy--] = data[i];
for (; j >=start + length + 1; --j)
copy[indexCopy--] = data[j];
return left + right + count;
}
int InversePairs(int* data, int length)
{
if (data == NULL || length < 0)
return 0;
int *copy = new int[length];
for (int i = 0; i < length; i++)
copy[i] = data[i];
int count = InversePairsCore(data, copy, 0, length - 1);
delete[] copy;
return count;
}
int main()
{
int a[] = { 7, 5, 6, 4 };
cout << InversePairs(a, 4);
system("pause");
return 0;
}