/**
* author: tourist
* created:
**/
#include "shoes.h"
#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include "algo/debug.h"
#else
#define debug(...) 42
#endif
template <typename T>
class fenwick {
public:
vector<T> fenw;
int n;
fenwick(int _n) : n(_n) {
fenw.resize(n);
}
void modify(int x, T v) {
while (x < n) {
fenw[x] += v;
x |= (x + 1);
}
}
T get(int x) {
T v{};
while (x >= 0) {
v += fenw[x];
x = (x & (x + 1)) - 1;
}
return v;
}
};
long long count_swaps(vector<int> a) {
int n = a.size() / 2;
long long swaps = 0;
fenwick<int> fenw(2 * n);
map<int, deque<int>> mp;
for (int i = 0; i < 2 * n; i++) {
mp[a[i]].push_back(i);
}
for (int i = 0; i < 2 * n; i++) {
fenw.modify(i, 1);
}
set<int> unlock;
for (int i = 0; i < 2 * n; i++) {
unlock.insert(i);
}
for (int i = 0; i < 2 * n; i += 2) {
int p = mp[-a[*unlock.begin()]].front();
swaps += fenw.get(p - 1) + (a[*unlock.begin()] > 0) - 1;
fenw.modify(*unlock.begin(), -1);
fenw.modify(p, -1);
mp[a[*unlock.begin()]].pop_front();
mp[-a[*unlock.begin()]].pop_front();
unlock.erase(*unlock.begin());
unlock.erase(p);
}
return swaps;
}
// Version with comments:
// Basically, always swap the leftmost shoe with whatever matches.
// In order to simulate this process, we maintain a set of
// unlocked positions (whose order never changes, till they get
// paired with each other). And for the leftmost, we take
// *unlocked.begin(). Also, you need the # of swaps, which reduce
// to counting number of numbers < x (because there's nothing before
// *unlocked.begin()), and add 1 when you need the extra swap.
// Then, after each corrected pair, just update all your data structures.
