HackerRank "Components in a graph"

Regular Union-Find practice one.

#include <cmath>
#include <cstdio>
#include <climits>
#include <vector>
#include <iostream>
#include <fstream>
#include <algorithm>
#include <unordered_set>
#include <unordered_map>
using namespace std;

unordered_map<int, int> ps; // for id
unordered_map<int, unsigned> us; // for sets

int id(int v)
{    
    if(!ps.count(v)) return -1;
    
    while(ps[v] != v) v = ps[v];
    return v;
}

bool find_(int p0, int p1)
{
    return id(p0) == id(p1) && id(p0) != -1;
}

void union_(int v0, int v1)
{
    int p0 = id(v0), p1 = id(v1);
    if(p0 != -1 && p1 != -1) // 2 existing sets
    {
        if(p0 != p1)
        {
            int sp = min(p0, p1);
            int sl = max(p0, p1);
            ps[sl] = sp;
            
            us[sp] += us[sl];
            us.erase(sl);
        }
    }
    else // 1 is wild
    {
        int pv = p0 != -1 ? p0 : p1;
        int wv = p0 == -1 ? v0 : v1;
        ps[wv] = pv;
        us[pv]++;
    }
}

int main() 
{    

    int n; cin >> n;
    while(n--)
    {
        int a, b; cin >> a >> b;
        int s = min(a, b), l = max(a, b);    
        int is = id(s), il = id(l);
        
        if(is == -1 && il == -1)
        {
            ps[l] = ps[s] = s;            
            us[s] = 2;
        }
        else
        {
            if(!find_(s, l))
            {
                union_(s, l);
            }
        }
    }
    
    unsigned minv = INT_MAX, maxv = 0;
    for(auto &kv: us)
    {
        maxv = max(maxv, kv.second);
        minv = min(minv, kv.second);
    }
    cout << minv << " " << maxv << endl;
    return 0;
}