Hello codeforces ,

i'm brand new to dfs and i have spend like 4 hours trying to find a solution for The Tag Game problem.

what i have tried:

bob wants to maxmizes the solution , alice wants to minimize , so bob need to reach the deepest node , when bob reaches it alice will move to catch him , but bob has the choice to stay in the node (each of them has that option but i guess only bob will use it) i can't handle this choice of staying as a move, this is my code:

const int N_=10e5+6,M=2*10e5+6;
const int NOT_VISITED = 0 , IN_PROGRESS = 1 , VISITED = 2;
int m,n,u,v;
vector<int> adj[N_];
vector<pair<int,int>> dxdy = {{-1,0},{1,0},{0,1},{0,-1}};
// vector<vector<bool>> vis;
bool vis[N_];
int c;

// bool isValid(int x , int y , vector<STR>&grid){
//    if(x < 0 || x > n-1 || y <0 || y>m-1) return false;
//    if(vis[x][y] || grid[x][y] == '#') return false;
//    return true;
// }
int md = 0 , fn=0;
void dfs(int u,int depth){
   vis[u] =true;
   if(depth > md){
      md = depth;
      fn = u;
   }
   c++;
   for(auto x : adj[u]){
      if(!vis[x]){
         dfs(x,depth+1);
      }
   }
}

void solve()
{
   cin >> n>>m;
   for(int x = 0 ;x < n-1 ; x++){
      cin >>u >>v;
      adj[u].push_back(v);
      adj[v].push_back(u);
   }
   dfs(m,0);
   int ans = md;
   memset(vis,false,sizeof(vis));
   md=0;
   c=0;
   dfs(1,0);
   c-=2;
   cout << ans+c+md;
   
}

Hello CF , First thing first , happy new year , May this year bring you health , happiness and successes in all you do !

i have struggled to understand Palindrome Pairs solution "in terms of bitmasks" , as i'm newbie.

i didn't thought about the iterative solution as it will be o(n^2) which will case TLE ,so i was trying to get a better solution and i wasn't able to , so i saw the solution which is something like this:

int main()
{
   FastIO;
   ll n ;cin >>n;
   map<ll,ll> mp;
   ll ans = 0;
   while(n--)
   {
      STR s;cin>>s;
      ll m = 0;
      for(auto x : s)
      {
         ll v = x-'a';
         m ^= (1 << v);
      }
      ans += mp[m];
      for(int x = 0 ; x < 26 ; x++)
      {
         m ^= (1 << x);
         ans += mp[m];
         m ^= (1 << x);
      }
      mp[m]++;
   }
   cout << ans;
}

i don't get it , i mean i know to check if a string is a Palindrome or not we get it's mask and check it's power of 2 or not by XOR'ing the values of each char ....help

Hello codeforces, as i have learned a new datastructure , i would like to solve some problems on it , so suggest some problems i can solve on binary search trees.

Hello , Recently i was trying to solve this problem 932B which was kinda tricky as it requires prefix sum to avoid TLE , it required 2d-prefix sum , so what's that and why i could need it , suggest some problems to get familiar with it.

Hello , suggest any problem (or set of problems) that can be solved using recursion and it's grid based , problems like go from s to e , or find the shortest path .... etc

Hello codeforces , a few days ago i started learning more about recursion , and i indeed tried to solve some very basic problems on it , however , when it comes to tricky problems i cannot think how to implement a recursive function to solve the problem , another thing makes me wondring is when should i implement a recursive function and when i use the iterative function, so if anyone has some ideas about the previous questions , write it below.

thanks.

Hello , when solving problems on binary search, i solve them because i know that i'm solving problems on Binary search topic , but if i come to a problem statement i don't know how or even if I should use binary search or not ... so my question is , how to make sure you're solving a binary search problem?

Hello codeforces , i just have learned the backtracking technique , i want to practice and put my hands on , i want some biggener freindly problems

Hello , Could some one please suggest a set of problems i can solve to put my hands on the "Coordinates Compression" technique ?