# ALGI Exordium: Editorial
[**Exordium**](https://codeforces.com/contestInvitation/7ed15875b6ee8cac2dd8aef7713b1b41cc9a7401) là **Tuyển tập 25 Bài Code Nhập môn** (chọn lọc từ sách **300 bài code thiếu nhi**) do [**The Algitect** (ALGI Project)](https://www.facebook.com/algitect.project) sinh test chấm nhằm hỗ trợ các bạn học sinh mới học lập trình nắm chắc cách sử dụng ngôn ngữ lập trình (đặc biệt là ở bậc THCS).
[toc]
## Phân loại: Tính toán cơ bản - Câu điều kiện - Vòng lặp
### Problem [01]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main(){
long long a, b;
cin >> a >> b;
cout << a + b << '\n';
cout << a - b << '\n';
cout << b - a << '\n';
cout << a * b;
return 0;
}
```
:::
### Problem [02]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main() {
int a, b, c, t;
cin >> a >> b >> c;
if (a < b) {
t = a;
a = b;
b = t;
}
if (a < c) {
t = a;
a = c;
c = t;
}
if (b < c) {
t = b;
b = c;
c = t;
}
cout << c << ' ' << b << ' ' << a;
return 0;
}
```
:::
### Problem [03]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main(){
long long a, b;
cin >> a >> b;
cout << (-b) / a;
return 0;
}
```
:::
### Problem [04]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main(){
long long hour;
cin >> hour;
long long week = 24*7, day = 24;
cout << hour / week << " ";
hour %= week;
cout << hour / day << " ";
hour %= day;
cout << hour << " ";
return 0;
}
```
:::
### Problem [05]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main() {
long long d, m, y, top;
cin >> d >> m >> y;
if (m < 1 || m > 12) {
cout << "Khong hop le";
return 0;
}
if (m == 4 || m == 6 || m == 9 || m == 11) {
top = 30;
}
else if (m == 2) {
top = 28;
if ((y % 4 == 0 && y % 100 != 0) || y % 400 == 0) {
top++;
}
}
else {
top = 31;
}
if (d < 1 || d > top) {
cout << "Khong hop le";
return 0;
}
cout << "Hop le";
return 0;
}
```
:::
### Problem [06]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main() {
int h, m, s, timer;
cin >> h >> m >> s;
timer = 3600 * h + 60 * m + s;
cin >> h >> m >> s;
timer -= 3600 * h + 60 * m + s;
if (timer < 0) timer = -timer;
cout << timer / 3600 << " ";
cout << (timer % 3600) / 60 << " ";
cout << (timer % 3600) % 60;
return 0;
}
```
:::
### Problem [07]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main() {
int n;
cin >> n;
int count = 0;
long long sum = 0;
for (int i = 1; i <= n; i++) {
if (n % i == 0) {
cout << i << " ";
count++;
sum += i;
}
}
cout << count << "\n" << sum;
return 0;
}
```
:::
### Problem [08]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main() {
long long n, t;
long long u, sum = 0, count = 0;
cin >> n;
t = n;
do {
count++;
u = t % 10;
sum += u;
}
while (t /= 10);
do {
t = t * 10 + n % 10;
}
while (n /= 10);
cout << count << "\n";
cout << n % 10 << "\n";
cout << u << "\n";
cout << sum << "\n";
cout << t;
return 0;
}
```
:::
### Problem [09]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main() {
long long a, b;
cin >> a >> b;
cout << __gcd(a, b) << "\n";
cout << a / __gcd(a, b) * b;
return 0;
}
```
:::
### Problem [10]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main() {
double xA, yA, xB, yB;
cin >> xA >> yA >> xB >> yB;
double res = sqrt((xB - xA) * (xB - xA) + (yB - yA) * (yB - yA));
cout << fixed << setprecision(4) << res;
return 0;
}
```
:::
## Phân loại: Tính toán nâng cao - Mảng một chiều
### Problem [11]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int n, res;
bool check(int x) {
for (int j = 2; j < x; j++) {
if (x % j==0) {
return false;
}
}
return true;
}
int main() {
cin >> n;
for (int i = 2; ; i++){
if (check(i)) {
cout << i << " ";
res++;
}
if (res == n) break;
}
return 0;
}
```
:::
### Problem [12]
:::success
```cpp = 1
```
:::
### Problem [13]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int n, res;
int main() {
cin >> n;
for (int a = 1; a <= n; a++) {
for (int b = a+1; b <= n; b++) {
for (int c = b+1; c <= n; c++) {
if (a*a + b*b == c*c) {
res++;
}
}
}
}
cout << res;
return 0;
}
```
:::
### Problem [14]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int main() {
int n;
cin >> n;
if (n % 2 != 0) {
cout << ((1 + n) * ((n + 1) / 2)) / 2;
}
else {
cout << ((2 +n ) * (n / 2)) / 2;
}
return 0;
}
```
:::
### Problem [15]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
const int N = 1e6;
int n, m, q, res;
int A[N+5];
int main() {
cin >> n >> q;
for (int i = 1; i <= n; i++) {
cin>>A[i];
}
for (int i = 1; i <= q; i++) {
int id, x;
cin >> id >> x;
A[id] = x;
}
for (int i = 1; i <= n; i++) {
cout << A[i] << " ";
}
return 0;
}
```
:::
### Problem [16]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
const int N = 1e6;
int n, m, q, k;
double res, ans;
int A[N+5];
int main() {
cin >> n >> k;
for (int i = 1; i <= n; i++) {
cin >> A[i];
res += A[i];
}
for (int i = 1; i <= k; i++) {
int x;
cin >> x;
ans += A[x];
}
cout << fixed << setprecision(5) << (res / n) << "\n";
cout << fixed << setprecision(5) << (ans / k);
return 0;
}
```
:::
### Problem [17]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
const int N = 1e6;
int n, m, q, k;
int A[N*2+5];
int main() {
cin >> n >> k;
for (int i = 1; i <= n; i++) {
cin >> A[i];
A[i+n] = A[i];
}
k %= n;
for (int i = 1+k; i <= k+n; i++) {
cout << A[i] << " ";
}
cout << "\n";
for(int i= n-k+1; i <= n-k+n; i++) {
cout << A[i] << " ";
}
return 0;
}
```
:::
### Problem [18]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
const int N = 1e6;
int n, m, q, k, sl1, gt1, sl2 = INT_MAX, gt2;
long double res, ans;
int A[N+5], D[N+5];
int main() {
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> A[i];
D[A[i]]++;
}
for (int i = 1; i <= n; i++) {
int x = A[i];
if (D[x] > sl1){
sl1 = D[x];
gt1 = x;
}
if (D[x] == sl1) {
gt1 = max(gt1,x);
}
if (D[x] < sl2) {
sl2 = D[x];
gt2 = x;
}
if (D[x]==sl2) {
gt2 = min(gt2,x);
}
}
cout << gt1 << " " << sl1 << "\n";
cout << gt2 << " " << sl2;
return 0;
}
```
:::
### Problem [19]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
const int N = 5e6;
int n;
bool check[N+5];
int main() {
cin >> n;
for (int i = 2; i*i <= n; i++) {
if (check[i] == false) {
for (int j = i*i; j<=n; j+=i) {
check[j] = true;
}
}
}
for (int i = 2; i <= n; i++) {
if (check[i] == false) {
cout << i << " ";
}
}
return 0;
}
```
:::
### Problem [20]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
const int N = 1e6;
const long long M = 1e9 + 7;
int n;
long long F[N+1];
int main() {
F[1] = 1;
F[2] = 1;
cin >> n;
for (int i = 3; i <= n; i++) {
F[i] = (F[i-1] + F[i-2]) % M;
}
cout << F[n];
return 0;
}
```
:::
## Phân loại: Khác
### Problem [21]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
const int N = 1e5;
int n, k, A[N+1];
int main() {
cin >> n >> k;
for (int i = 1; i <= n; i++) {
cin >> A[i];
}
sort(A+1, A+1+n);
cout << A[k] << " " << A[n-k+1];
return 0;
}
```
:::
### Problem [22]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
const int N = 1e3;
int n, m, q, A[N+1][N+1];
int main() {
cin >> n >> m;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cin >> A[i][j];
}
}
cin >> q;
while (q--) {
int i, j, x;
cin >> i >> j >> x;
A[i][j] = x;
}
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cout << A[i][j] << " ";
}
cout << "\n";
}
return 0;
}
```
:::
### Problem [23]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
string s; char k;
int main() {
cin >> s >> k;
for (int i = 0; i < s.size(); i++) {
if (s[i] == k) {
cout << (i+1) << " ";
}
}
return 0;
}
```
:::
### Problem [24]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
string s;
int main() {
cin >> s;
for (int i = 0; i < s.size()/2; i++) {
if (s[i] != s[s.size() - i - 1]) {
cout << "No";
return 0;
}
}
cout << "Yes";
return 0;
}
```
:::
### Problem [25]
:::success
```cpp = 1
#include <bits/stdc++.h>
using namespace std;
int n;
void solve(int n, char s, char t, char mid) {
if (n == 1) {
cout << 1 << " " << s << " " << t << "\n";
return;
}
solve(n - 1, s, mid, t);
cout << n << " " << s << " " << t << "\n";
solve(n - 1, mid, t, s);
}
int main() {
cin >> n;
solve(n, 'A', 'C', 'B');
return 0;
}
```
:::
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