C++ DFS，内存限制

我的代码解决了这个问题：

为什么通过引用 DFS 传递数组会导致内存限制，但全局声明它们会通过所有测试？

错误解决方法：

#include <bits/stdc++.h>

using namespace std; 

vector <int> res;
int n, m;
void dfs(int v, vector<vector<int>> graph, vector<int> &used, vector<pair<int, int>> edges)
{
    used[v] = 1;

    for(int u:graph[v])
    {
        if(used[u] == 0)
        {
            for(int j = 1;j <= m;j++)
            {
                pair<int, int> p1 = {u, v};
                pair<int, int> p2 = {v, u};
                if(edges[j] == p1 || edges[j] == p2){
                    res.push_back(j);
                    break;
                } 
            }
            dfs(u, graph,  used, edges);
        }
    }
}
int main()
{
    int ind = 1;
    cin >> n >> m;
    vector <vector<int>> graph(n+1);
    vector <int> used(n+1, 0);
    vector <pair<int, int>> edges(m+1);

    for(int i = 0;i < m;i++)
    {
        int t1, t2;
        cin >> t1 >> t2;
        graph[t1].push_back(t2);
        graph[t2].push_back(t1);
        edges[ind] = {t1, t2};
        ind++;
    }
    dfs(1, graph,  used, edges);
    
    cout << res.size() << endl;
    for(int x:res) cout << x << " ";

}