1830A - Copil Copac Draws Trees - CodeForces Solution

#include <bits/stdc++.h>

using namespace std;
vector<pair<int, int>>M[200001];
int id[200001];
int dp[200001];
bool biju[200001];
DFS(int v)
{
    biju[v]=1;
    for(auto c : M[v])
    {
        if(biju[c.first]!=1)
        {
            if(id[v]<=c.second&&id[v]!=0)
            {
                id[c.first]=c.second;
                dp[c.first]=dp[v];
            }
            else
            {
                id[c.first]=c.second;
                dp[c.first]=dp[v]+1;
            }
            DFS(c.first);
        }
    }
}
int main()
{
    int n;
    cin>>n;
    for(int i=0; i<n; i++)
    {
        int m, a, b, mx=0;
        cin>>m;
        for(int l=1; l<=m-1; l++)
        {
            cin>>a>>b;
            M[a].push_back({b, l});
            M[b].push_back({a, l});
        }
        id[1]=0;
        dp[1]=0;
        DFS(1);
        for(int l=1; l<=m; l++)
        {
            if(dp[l]>mx)
            {
                mx=dp[l];
            }
        }
        cout<<mx<<'\n';
        for(int l=1; l<=m; l++)
        {
            M[l].clear();
            biju[l]=0;
            dp[l]=0;
            id[l]=0;
        }
    }
    return 0;
}