#include "shoes.h"
#include <algorithm>
#include <vector>
using namespace std;
// Fenwick tree
void update(vector<int> &fenwick, int index, int value) {
while (index < (int)fenwick.size()) {
fenwick[index] += value;
index += index & -index;
}
}
int getSum(const vector<int> &fenwick, int index) {
int sum = 0;
while (index) {
sum += fenwick[index];
index -= index & -index;
}
return sum;
}
// Reverse fenwick tree for suffix sums
void updateR(vector<int> &fenwick, int index, int value) {
update(fenwick, (int)fenwick.size()-index, value);
}
int getSumR(const vector<int> &fenwick, int index) {
return getSum(fenwick, (int)fenwick.size()-index);
}
long long count_swaps(vector<int> s) {
int n = (int)s.size() / 2;
vector<vector<int>> nxt[2];
nxt[0] = nxt[1] = vector<vector<int>>(1+n);
for (int i = 2*n-1; i >= 0; --i) {
if (s[i] < 0) nxt[0][-s[i]].push_back(i);
else nxt[1][s[i]].push_back(i);
}
vector<int> fenwickMoved(1+2*n);
vector<bool> paired(2*n);
long long swaps = 0;
for (int i = 0; i < 2*n; ++i) {
if (paired[i]) continue;
int v = abs(s[i]), side = s[i] > 0;
int j = nxt[1-side][v].back();
swaps += (j + getSumR(fenwickMoved, j+1)) - (i + getSumR(fenwickMoved, i+1));
if (!side) --swaps; // do not need to swap with each other
updateR(fenwickMoved, j+1, +1);
paired[i] = true, paired[j] = true;
nxt[0][v].pop_back(), nxt[1][v].pop_back();
}
return swaps;
}
