Depth First Search DFS (code (C++)

This algorithm can transverse a graph and find all the reachable points

 1  #include<bits/stdc++.h>

 2  using namespace std;

 3  int n,e;

 4  vector<int>g[128];

 5  bool seen[128];

 6 

 7  void dfs(int u){

 8  seen[u] = true;

 9  cout<<u<<" ";

10  for(int i=0;i<g[u].size();i++){

11      int v = g[u][i];

12      if(!seen[v])dfs(v);

13  printf("\n");

14  }

15 

16  }

17  int main(){

18  cin>>n>>e;

19  for(int i=0;i<n;i++){

20      int u,v;

21      cin>>u>>v;

22      g[u].push_back(v);

23  }

24  for(int i = 1;i<=n;i++ ){

25      if(!seen[i]){

26          dfs(i);

27      }

28  }

29 

30  return 0;}

Finding Array of Prime and Factors using Sieve of Eratosthenes Algorithm in C++

Theory: Using the sieve of Eratosthenes find an array of prime numbers.

Explanation:

1.Declare an int array sieve[]
2.Using the Sieve of Eratosthenes algorithm an array of prime can be obtained.Again factors of non prime can also be obtained;
3.sieve[i] == 0 : i is a prime number.
4. When not equal to zero the factor is displaced within the array element.

Code
#include <bits/stdc++.h>
using namespace std;
int sieve[100];
int main(){
int n;

cin>>n;
for(int x=2; x<=n; x++){
if(sieve[x]){
continue;
}
for(int i=2*x;i<=n;i+=x){
sieve[i]=x;
}
}

cout<<"Prime factors is those elements with 0 and other elements are factors";
for(int i=2;i<=n;i++){

    cout<<i<<" "<<sieve[i]<<endl;
}
return 0;}