CSES : Algorithm for problem solving 2020 WEEK 1 (c++)

https://cses.fi/alon20/list/

CSES - Algoritmit ongelmanratkaisussa 2020 - Tasks

Sum

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ar array

ll N;

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

    cin>>N;

    ll ans = 1ll*(N*(N+1))/2;
    cout<<ans;
	return 0;
}

List

#include <bits/stdc++.h>
using namespace std;

#define ll long long

int N;
list <int> ans;

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

    cin>>N;
    if(N==1){
        cout<<1;
        return 0;
    }
    if(N<4){
        cout<<"NO SOLUTION";
        return 0;
    }

    ans.push_back(2);
    ans.push_back(4);
    ans.push_back(1);
    ans.push_back(3);
    ans.push_back(5);
    for(int i=6;i<=N;i++){
        if(i%2==0){
            ans.push_front(i);
        }else{
            ans.push_back(i);
        }
    }
    
    list<int>::iterator it;
    for(auto it=ans.begin();it!=ans.end();it++){
        cout<<*it<<" ";
    }

	return 0;
}

Palindrome

#include <bits/stdc++.h>
using namespace std;

#define ll long long

int alphabet[26];
string al;
int chk;
list <char> solf,solm,solb;

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

    cin>>al;

    for(int i=0;i<al.size();i++){
        alphabet[al[i]-'A']++;
    }
    for(int j=0;j<26;j++){
        char a = j+'A';
        if(chk>=2){
            cout<<"NO SOLUTION";
            return 0;
        }
        int temp = alphabet[j]%2;
        int f = alphabet[j]/2;
        if(temp==0){
            for(int i=0;i<f;i++){
                solf.push_back(a);
                solb.push_front(a);
            }
        }else{
            for(int i=0;i<f;i++){
                solf.push_back(a);
                solb.push_front(a);
            }
            solm.push_back(a);
            chk++;
        }
    }
    for(auto it=solf.begin();it!=solf.end();it++){
        cout<<*it;
    }
    for(auto it=solm.begin();it!=solm.end();it++){
        cout<<*it;
    }
    for(auto it=solb.begin();it!=solb.end();it++){
        cout<<*it;
    }

	return 0;
}

Pinot

#include <bits/stdc++.h>
using namespace std;

#define ll long long

int N;

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
    cin>>N;
    for(ll i=0,a,b;i<N;i++){
        cin>>a>>b;
        if(a>2*b||b>2*a)  cout<<"NO"<<"\n";
        else if((a+b)%3==0) cout<<"YES"<<"\n";
        else cout<<"NO"<<"\n";
    }

	return 0;
}