建议评红

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double db;
ll l, r;
int main() {
    cin >> l >> r;
    ll sum = 0;
    for (ll i = l; i <= r; i++) {
        ll k = i;
        while (k > 0) {
            if (k % 10 == 2)
                sum++;
            k /= 10;
        }
    }
    cout << sum << endl;
    return 0;
}

主要是数位分离