Vector Stack Pair | Longest path in a tree using dfs

Question

#include <bits/stdc++.h>
using namespace std;

vector <int> adj(10001);
bool vis[10001];

void initialize ()
{
    for (int i = 0; i<10001; i++)
        vis[i] = false;
}

pair <int,int> dfs ( int x )
{
    stack < pair<int,int> > s;
    s.push( make_pair (x,0) );
    int maxnode = x, maxlevel = 0;

    while (!s.empty())
    {
        int t = s.top().first;
        int level = s.top().second;
        if (level>maxlevel)
        {
            maxnode = t;
            maxlevel = level;
        }

        s.pop();
        vis[t] = true;

        for ( int i = 0; i<adj[t].size(); i++)
        {
            if ( vis[adj[t][i]]==false)
            {
                s.push( make_pair (adj[t][i], level+1 ));
            } 
        }

    }

    return make_pair (maxnode,maxlevel);
}

int main() {
    // your code goes here
    int n, x;
    cin>>n;

    if (n==1 || n==2)
    {
        cout<<n-1;
        exit(0);
    }

    initialize();

    for (int i = 0; i<n-1; i++)
    {
        int a, b;
        cin>>a>>b;

        if (i==0)
            x = a;

        adj[a].push_back(b);
        adj[b].push_back(a);
    }

    pair <int,int> far1 = dfs (x);
    initialize();
    pair <int,int> far2 = dfs (far1.first);

    cout<<far2.second;


    return 0;
}

Or the code is here.

Error related to vector, stack, pair:

prog.cpp: In function 'std::pair dfs(int)': prog.cpp:32:29: error: request for member 'size' in 'adj.std::vector<_Tp, _Alloc>::operator[] >(((std::vector::size_type)t))', which is of non-class type '__gnu_cxx::__alloc_traits >::value_type {aka int}' for ( int i = 0; i ^ prog.cpp:34:21: error: invalid types '__gnu_cxx::__alloc_traits >::value_type {aka int}[int]' for array subscript if ( vis[adj[t][i]]==false)
^ prog.cpp: In function 'int main()': prog.cpp:66:10: error: request for member 'push_back' in 'adj.std::vector<_Tp, _Alloc>::operator[]>(((std::vector::size_type)a))', which is of non-class type '__gnu_cxx::__alloc_traits >::value_type {aka int}' adj[a].push_back(b);
^ prog.cpp:67:10: error: request for member 'push_back' in 'adj.std::vector<_Tp, _Alloc>::operator[]>(((std::vector::size_type)b))', which is of non-class type '__gnu_cxx::__alloc_traits >::value_type {aka int}' adj[b].push_back(a);
^

Please help me rectify these.

Jyotiraditya Jyotiraditya · Accepted Answer · 2018-08-15T16:01:51

Solved: vector adj(10001); to vector adj[10001]; as it was a 2d vector

Vector Stack Pair | Longest path in a tree using dfs

1 Answers