Adding Codechef September2020 Lunchtime (sastava007#9)

Added Codechef September 2020 Lunchtime.

Author: skrishan07

Codechef/SEPT2020-LUNCHTIME/GCD operations.cpp

@@ -0,0 +1,49 @@
+#include<bits/stdc++.h>
+#define ll long long int
+using namespace std;
+int gcd(int a, int b)
+{
+    if (b == 0)
+        return a;
+    return gcd(b, a % b);    
+}
+int main()
+{
+	ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+	int tc,n,flag,v;
+	cin>>tc;
+	while(tc--)
+	{
+		flag=1;
+		cin>>n;
+		vector<int>a(n);
+		vector<int>b(n);
+		for(int i=0;i<n;i++)
+		{
+			a[i]=i+1;
+			cin>>b[i];
+	    }
+	    for(int i=0;i<n;i++)
+	    {
+	    	if(a[i]!=b[i] && b[i]!=1)
+	    	{
+	    		v=gcd(a[i],b[i]);
+	    		if(v!=b[i])
+	    		{
+	    			flag=0;
+	    			break;
+				}
+			}
+		}
+		if(flag==0)
+		{
+			cout<<"NO"<<endl;
+		}
+		else
+		{
+			cout<<"YES"<<endl;
+		}
+	}
+	return 0;
+}

Codechef/SEPT2020-LUNCHTIME/Root the Tree.cpp

@@ -0,0 +1,61 @@
+#include<bits/stdc++.h>
+#define ll long long int
+using namespace std;
+void dfs(vector<int>a[], int n, bool visited[], int &ans, bool root[])
+{
+	visited[n]=true;
+	for(int i=0;i<a[n].size();i++)
+	{
+		if(!visited[a[n][i]])
+		{
+			dfs(a,a[n][i],visited,ans,root);
+		}
+		else
+		{
+			if(root[ a[n][i] ]==true)
+			{
+				root[a[n][i]]=false;
+			}
+			else
+			{
+				ans++;
+			}
+		}
+	}
+}
+int main()
+{
+	ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+	int tc,n,x,y,ans;
+	cin>>tc;
+	while(tc--)
+	{
+		ans=0;
+		cin>>n;
+		vector<int>a[n+1];
+		bool visited[n+1];
+		bool root[n+1];
+		for(int i=1;i<n;i++)
+		{
+			visited[i]=false;
+			cin>>x>>y;
+			a[x].push_back(y);
+		}
+		for(int i=0;i<=n;i++)
+		{
+			visited[i]=false;
+			root[i]=false;
+		}
+		for(int i=1;i<=n;i++)
+		{
+			if(visited[i]==false)
+			{
+				root[i]=true;
+				dfs(a,i,visited,ans,root);
+			}
+		}
+		cout<<ans<<endl;
+	}
+	return 0;
+}

Codechef/SEPT2020-LUNCHTIME/Watermelon.cpp

@@ -0,0 +1,30 @@
+#include<bits/stdc++.h>
+#define ll long long int
+using namespace std;
+int main()
+{
+	ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+	int tc,n,sum,x;
+	cin>>tc;
+	while(tc--)
+	{
+		sum=0;
+		cin>>n;
+		vector<int>a(n);
+		for(int i=0;i<n;i++)
+		{
+			cin>>a[i];
+			sum+=a[i];
+		}
+		if(sum>=0)
+		{
+			cout<<"YES"<<endl;
+		}
+		else
+		{
+			cout<<"NO"<<endl;
+		}
+	}
+	return 0;
+}