DSU-НепересекающиесяМножества

#include <iostream>
#include <string>
#include <vector>

using namespace std;

class DSU
{
public:
    vector<int> parent;
    DSU(int N)
    {
        parent.resize(N, -1);
    }

    int find(int v)
    {
        int r = v;

        while (parent[r] != -1)
        {
            r = parent[r];
        }

        while (parent[v] != -1)
        {
            int tmp = v;
            v= parent[v];
            parent[tmp] = r;
        }

        return r;
    }

    void unio (int i, int j)
    {
        int ri = find(i);
        int rj = find(j);
        parent[ri] = rj;
    }
};

int main()
{
    int N = 0, M = 0;
    cin >> N >> M;
    DSU dsu(N + 1);
    int from = 0, to = 0, cnt = 0;
    for (int i = 0; i < M; i++)
    {
        cin >> from >> to;
        cnt++;
        if (dsu.find(from) != dsu.find(to))
        {
            dsu.unio (from, to);
            N--;
        }
        if (N == 1)
            break;
    }

    cout << cnt;
    return 0;
}