#include <bits/stdc++.h>
using namespace std;
void prepareAdj(vector<pair<int, int>>&edges,unordered_map<int,list<int>>&adj){
    for(int i=0;i<edges.size();i++){
        int u = edges[i].first;
        int v = edges[i].second;
        adj[v].push_back(u);
        adj[u].push_back(v);
    }

}
vector<int> BFS(int vertex, vector<pair<int,int>> edges)
{
    unordered_map<int,list<int>>adj;
    vector<int>ans;
    prepareAdj(edges,adj);
    map<int,bool>visited;
    queue<int>q;
    q.push(vertex);
    visited[vertex]=true;
    while(!q.empty()){
        int filhal = q.front();
        ans.push_back(filhal);
        q.pop();
        for(auto i: adj[filhal]){
            if(!visited[i]){
                q.push(i);
                visited[i]=true;
            }
        }
    }
    return ans;
}
int main(){
  int n,m;
  cin>>n>>m;
  vector<pair<int,int>>edges(m);
  for(int i=0;i<m;i++){
    int a,b;
    edges.push_back({a,b});
  }
  
 vector<int>qqq= BFS(0,edges);
 for(auto i: qqq){
   cout<<i<<" ";
 }
}
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Write, Run & Share C++ code online using OneCompiler's C++ online compiler for free. It's one of the robust, feature-rich online compilers for C++ language, running on the latest version 17. Getting started with the OneCompiler's C++ compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as C++ and start coding!

Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}