# **Contest Hè**

**Link Submit:** [**HERE**](http://qboj.zapto.org/contest/cthe01)

# 696969696969696969696969

#### **SOLUTION**

:::spoiler C++

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


int n;
int main(){
    ios_base::sync_with_stdio(0); 
    cin.tie(nullptr); cout.tie(nullptr);
    cin >> n;
    if (n % 9 != 0) cout <<n % 9;
    for (int i = 0; i < n / 9; i++) cout <<9;
    return 0;
}

:::
---
# Tổng Dãy Con

#### **SOLUTION**

:::spoiler C++

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


const int maxn = 1e5 + 5;


int n, q;
long long pre[maxn];
int main(){
    ios_base::sync_with_stdio(0); 
    cin.tie(nullptr); cout.tie(nullptr);
    cin >>n >>q;
    for (int i = 1; i <= n; ++i){
        int x; cin >>x;
        pre[i] = pre[i - 1] + x * (x > 0);
    }
    while (q--){
        int l, r; cin >>l >>r;
        cout <<pre[r] - pre[l - 1] <<'\n';
    }
}

:::
---
# Một Bài Toán Của Đề HSG Chỗ Mô Đó

#### **SOLUTION**
:::spoiler C++

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


bool check(string s){
    int sum = 0;
    bool k = 0;
    f0(i, n){
        (sum += s[i] - '0') %= 3;
        if (s[i] == '0') k = 1;
    }
    return !sum && k;
}

string s;
int n;
int main(){
    ios_base::sync_with_stdio(0); 
    cin.tie(nullptr); cout.tie(nullptr);
    cin >>n >>s;
    if (check(s)) sort(s.begin(), s.end(), greater<char>()), cout <<s;
        else cout <<-1;
}

:::
---
# Số Lẻ VCL ( Vô Cùng Luôn )

#### **SOLUTION**
:::spoiler C++

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


int n, res;
int main() {
    ios_base::sync_with_stdio(0); 
    cin.tie(nullptr); cout.tie(nullptr);
    cin >>n;
    while (n--){
        int x; cin >>x;
        res ^= x;
    }
    cout <<res;
    return 0;
}

:::
---
# Bán Nguyên Tố

#### **SOLUTION**
:::spoiler C++

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


const int lim = 1e6;

vector<bool> prime (lim + 1, 1);

void sieve(){
    prime[0] = prime[1] = 0;
    for(int i = 2; i <= lim / i; ++i) if (prime[i]) 
        for (int j = i * i; j <= lim; j += i) prime[j] = 0;
}

bool ok(ll x){
    ll sqx = sqrt(x);
    return prime[sqx] && sqx * sqx == x;
}
int n, res;
int main() {
    ios_base::sync_with_stdio(0); 
    cin.tie(nullptr); cout.tie(nullptr);
    sieve();
    int q; cin >>q;
    while (q--){
        ll x; cin >>x;
        cout <<ok(x) <<'\n';
    }
    return 0;
}