btwr.cpp

#include <iostream>
using namespace std;
const int nmax = 21;
int main() {
    int n;
    cin >> n;
    int a[nmax];
    int b[nmax];
    for(int i = 0; i < n; i++) {
        cin >> a[i] >> b[i];
    }

    for(int i = 0; i < n - 1; i++) {
        for(int j = i+1; j < n; j++) {
            if(a[i] < a[j]) {
                int ta = a[i]; int tb = b[i];
                a[i] = a[j]; b[i] = b[j];
                a[j] = ta; b[j] = tb;
            }
        }
    }
    int f[nmax];
    f[0] = 1;
    int lmax = 1;
    for(int i = 1; i < n; i++) {
        int max = 0;
        for(int j = 0; j < i; j++) {
            if(b[j] > b[i] && a[j] > a[i]&& f[j] > max) max = f[j];
        }
        f[i] = max + 1;
        if (f[i] > lmax) lmax = f[i];
    }
    cout << lmax;
    
    return 0;
}

change.cpp

#include <bits/stdc++.h>
using namespace std;
const int maxn = 11;
const int maxf = 1001;
const int inf = 999999;

int main() {
    freopen("testcase", "r", stdin);
    
    int c, n;
    cin >> c >> n;
    int a[maxn];
    int f[maxf];
    for(int i = 1; i <= n; i++) {
        cin >> a[i];
    }
    
    for(int i = 0; i <= n; i++) {
        for(int j = 0; j <= c; j++) {
            if(j == 0) f[j] = 0;
            else if(i == 0) f[j] = inf;
            else f[j] = min(f[j], f[j - a[i]] + 1);
        }
    }
    
    cout << f[c];
    
    return 0;
}

qprime.cpp

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

int main()
{
    int L, R, digit;
    cin >> L >> R >> digit;

    vector<bool> isPrime(R - L + 1, true);

    for (int i = 2; i * i <= R; ++i) {
        for (int j = max(i * i, (L + i - 1) / i * i); j <= R; j += i) {
            isPrime[j - L] = false;
        }
    }
    if (1 >= L) {
        isPrime[1 - L] = false;
    }

    int ans = 0;
    for (int x = L; x <= R; ++x) {
        if (isPrime[x - L]) {
            int t = x;
            while(t > 0) {
                if(t % 10 == digit) {
                    ans++;
                    break;
                }
                t /= 10;
            }
        }
    }
    cout << ans;
    return 0;
}