class Solution {
public:
    int minSwapsCouples(vector<int>& row) {
        int n = row.size() / 2, res = 0;
        unordered_map<int, int> map;
        unordered_set<int> path, visited;
        for(int i = 0; i < 2 * n; ++i)map[row[i]] = i;
        for(int i = 0; i < 2 * n; ++i)
            if(visited.find(i / 2) == visited.end())
                res += findCycle(row, map, path, visited, i) - 1;
        return res;
    }

private:
    int findCycle(vector<int>& row, unordered_map<int, int>& map, unordered_set<int>& path, unordered_set<int>& visited, int to)
    {
        int slot = to / 2, next = map[row[to ^ 1] ^ 1];
        if(path.find(slot) != path.end())return path.size();
        if(visited.find(slot) != visited.end())return 0;

        visited.insert(slot);
        path.insert(slot);
        int size = findCycle(row, map, path, visited, next);
        path.erase(slot);
        return size;
    }
};