# DFS approach in C++

#1
``````//This function determines the number of nodes connected to a particular node
void helper(unordered_map<int,vector<int>>&m,vector<bool>&vis,int curr,int &ans)
{
vis[curr]=true;
ans++;
for(auto it:m[curr])
{
if(!vis[it])
{
helper(m,vis,it,ans);
}
}
}
//This function determines at max how many edges can be removed. The logic is
//if any node including itself is having even number of descendants then the
// edge between this node and it's parent node can be removed safely.
void dfs(unordered_map<int,vector<int>>&m,vector<bool>&vis,vector<int>&count,int curr,int &edge)
{
vis[curr]=true;
for(auto it:m[curr])
{
if(!vis[it])
{
if(count[it]>0 && count[it]%2==0)
{
edge++;
}
dfs(m,vis,count,it,edge);
}
}
}
int Solution::solve(int A, vector<vector<int> > &B)
{
vector<int>count(A+1);// This vector keeps the track how many nodes are connected to a particular node
unordered_map<int,vector<int>>m;// The adjacency list of the graph
for(auto it:B)
{
m[it[0]].push_back(it[1]);
}
for(int i=1;i<=A;i++)// Filling up of count vector
{
vector<bool>vis(A+1,false);
int ans=0;
helper(m,vis,i,ans);
count[i]=ans;
}
vector<bool>vis(A+1,false);
int edge=0;
dfs(m,vis,count,1,edge);
return edge;
}

``````