归并排序&&树状数组求逆序数

归并排序：

#include <iostream>
#include <vector>
using namespace std;
vector<int>input,tmp(500005);
long long result;

void Merge(int left, int middle, int right)
{
int i, j, k;
i = left, j= middle+1, k = 1;
while(i<= middle && j <= right)
{
if(input[j] < input[i])
{
tmp[k++] = input[j++];
result += middle - i + 1;        
}
else
tmp[k++] = input[i++];
}
while(i <= middle)  tmp[k++] = input[i++];
while(j <= right) tmp[k++] = input[j++];

for(i = left, k = 1; i<= right; i++, k++)
input[i] = tmp[k];
}

void MergeSort(int left, int right)
{
if(right > left)
{
int middle = (right + left) / 2;
MergeSort(left,middle);
MergeSort(middle+1,right);
Merge(left,middle,right);
}
}

int main()
{
int m,n;
while(cin>>n)
{
if(n==0) break;
for(int i=0;i<n;i++)
{
cin>>m;
input.push_back(m);
}
result = 0;
MergeSort(0,n-1);
cout<<result<<endl;
input.clear();
}
}

树状数组：

#include <iostream>
#include <cstring>
using namespace std;

const int MAXN = 10005;
int in[MAXN];
int n;

int LowBit(int t)
{
return t&(-t);
}

int GetSum(int end)
{
int sum = 0;
while(end > 0)
{
sum += in[end];
end -= LowBit(end);
}
return sum;
}

void Plus(int pos, int num)
{
while(pos <= n)
{
in[pos] += num;
pos += LowBit(pos);
}
}

int main()
{
int x,sum;
while(cin>>n)
{
memset(in,0,sizeof(in));
sum = 0;
for(int i=1;i<=n;i++)
{
cin>>x;
sum += GetSum(n) - GetSum(x);
Plus(x,1);
}
cout<<sum<<endl;
}
}