Bai 12:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const long long nmax = 1e6;
ll tcs (ll n)
{
  ll s = 0;
  while(n)
  {
    s += n % 10;
    n /= 10;
  }
  return s;
}
ll x = 0, y = 1, z = 1, n;
int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);cout.tie(NULL);
  cin >> n;
  cout << "X = " << n % 10 << '\n';
  cout << "S(N) = " << tcs(n) << '\n';
  while (y != tcs(n))
  {
    ++y;
  }
  cout << "Y = " << y << '\n';
  while (tcs(n + z) != tcs(z) + tcs(n))
  {
    z++;
  }
  cout << "Z = " << z << '\n';
}

Bai 13:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const long long nmax = 1e6;
struct ans {
    int x, y, s;
};
ll a, b, c, d;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    cin >> a >> b >> c >> d;
    queue<ans> q;
    set<pair<int, int>> visited;
    q.push({a, b, 0});
    visited.insert({a, b});

    while (!q.empty()) {
        ans c1 = q.front();
        q.pop();
        if (c1.x == c && c1.y == d) {
            cout << c1.s;
            return 0;
        }

        vector<ans> t = {
            {c1.x + c1.y, c1.y, c1.s + 1},
            {c1.y, c1.x, c1.s + 1},
            {c1.x - c1.y, c1.y, c1.s + 1}
        };

        for (const auto& z : t) {
            if (z.x > 0 && z.y > 0 && visited.find({z.x, z.y}) == visited.end()) {
                q.push(z);
                visited.insert({z.x, z.y});
            }
        }
    }

    cout << -1; 
    return 0;
}