C++归并排序算法的应用：计算右侧小于当前元素的个数

template
class CTreeArr
{
public:
CTreeArr(int iSize) :m_vData(iSize+1)
{
}
void Add(int index, T value)
{
index++;
while (index < m_vData.size())
{
m_vData[index] += value;
index += index&(-index);
}
}
T Sum(int index)
{
index++;
T ret = 0;
while (index )
{
ret += m_vData[index];
index -= index&(-index);
}
return ret;
}
private:
vector m_vData;
};
class Solution {
public:
vector countSmaller(vector& nums) {
int iMin = *std::min_element(nums.begin(), nums.end());
for (auto& n : nums)
{
n -= iMin;
}
int iMax = *std::max_element(nums.begin(), nums.end());
CTreeArr treeArr(iMax + 1);
vector vRet(nums.size());
for (int i = nums.size() - 1; i >= 0; i–)
{
vRet[i] = treeArr.Sum(nums[i] - 1);
treeArr.Add(nums[i],1);
}
return vRet;
}
};

class CMergeSortIndex
{
public:
CMergeSortIndex(const vector& nums):m_nums(nums)
{
m_c = nums.size();
m_vIndexs.resize(nums.size());
iota(m_vIndexs.begin(), m_vIndexs.end(), 0);
}
void SortIndex( int left, int right)
{
if (right - left <= 1)
{
return;
}
const int mid = left + (right - left) / 2;
SortIndex( left, mid);
SortIndex( mid, right);
//nums的[left,mid) 和[mid,right)分别排序
vector vIndexs;
int i1 = left, i2 = mid;
while ((i1 < mid) && (i2 < right))
{
if (m_nums[m_vIndexs[i1]] > m_nums[m_vIndexs[i2]])
{
vIndexs.emplace_back(m_vIndexs[i2++]);
}
else
{
vIndexs.emplace_back(m_vIndexs[i1]);
OnAdd1(i1++, i2, left, mid, right);
}
}
while (i1 < mid)
{
vIndexs.emplace_back(m_vIndexs[i1]);
OnAdd1(i1++, i2, left, mid, right);
}
while (i2 < right)
{
vIndexs.emplace_back(m_vIndexs[i2++]);
}
for (int i = 0; i < vIndexs.size(); i++)
{
m_vIndexs[i + left] = vIndexs[i];
}
}
vector Sort()
{
SortIndex(0, m_c);
vector vRet(m_c);
for (int i = 0; i < m_c; i++)
{
vRet[i] = m_nums[m_vIndexs[i]];
}
return vRet;
}
protected:
virtual void OnAdd1(int i1, int i2, int left, int mid, int right) = 0;
int m_c;
const vector& m_nums;
vector m_vIndexs;
};
class CCountSmalle : public CMergeSortIndex
{
public:
CCountSmalle(const vector& nums):CMergeSortIndex(nums)
{
m_vRet.resize(m_c);
}
vector m_vRet;

};
class Solution {
public:
vector countSmaller(vector& nums) {
CCountSmalle test(nums);
auto tmp = test.Sort();
return test.m_vRet;
}
};