Mac Code Test

#include <iostream>
using namespace std;
 
int main() 
{
    cout << "Hello, World!";
    return 0;
}

#include <cstdio>
#include <iostream>
#include <vector>

using namespace std;

const int SIZE = 5e6 + 1;

struct edge
{
    int to_node, id;
    edge(int t, int i): to_node(t), id(i) {}
    ~edge() = default;
};

vector<int> edges[SIZE];
vector<edge> querys[SIZE];
int father[SIZE], mark[SIZE], ans[SIZE];

int n, m, s;

int getfa(int x)
{
    if (father[x] == x)
        return x;
    else
        return father[x] = getfa(father[x]);
}

void tarjan(int x)
{
    mark[x] = 1;
    for (auto i = edges[x].begin(); i != edges[x].end(); i++)
    {
        if (mark[*i])
            continue;
        tarjan(*i);
        father[*i] = x;
    }
    for (auto i = querys[x].begin(); i != querys[x].end(); i++)
    {
        int y = (*i).to_node, id = (*i).id;
        if (mark[y] == 2)
            ans[id] = getfa(y);
    }
    mark[x] = 2;
}

int main()
{
    int u, v;
    scanf("%d%d%d", &n, &m, &s);
    for (int i = 1; i <= n; i++)
    {
        father[i] = i;
        mark[i] = 0;
    }
    for (int i = 1; i < n; i++)
    {
        scanf("%d%d", &u, &v);
        edges[u].emplace_back(v);
        edges[v].emplace_back(u);
    }
    int x, y;
    for (int i = 1; i <= m; i++)
    {
        scanf("%d%d", &x, &y);
        if (x == y)
            ans[i] = 0;
        else
        {
            querys[x].emplace_back(edge(y, i));
            querys[y].emplace_back(edge(x, i));
        }
    }
    tarjan(s);
    for (int i = 1; i <= m; i++)
        printf("%d\n", ans[i]);
    return 0;
}