296B - Yaroslav and Two Strings - CodeForces Solution

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

#define ll long long
#define ld long double
#define ull unsigned long long
#define nl "\n"
#define vi vector<int>
#define vvi vector<vi>
#define vl vector<ll>
#define vvl vector<vl>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define setbits(x) __builtin_popcount(x)
#define zerobits(x) __builtin_ctzll(x)
#define all(a) (a).begin(), (a).end()
#define allr(a) (a).rbegin(), (a).rend()
#define ps(num, pre) fixed << setprecision(pre) << num
#define py cout << "Yes" << nl;
#define pn cout << "No" << nl;

ll mod = 1e9 + 7;

void ans1(bool x)
{
    if (x)
        cout << "Yes" << nl;
    else
        cout << "No" << nl;
}

ll power(ll a, ll b, ll m)
{
    a %= m;

    if (a == 0)
        return 0;
    ll res = 1;

    while (b > 0)
    {
        if (b & 1)
            res = (res * a) % m;
        a = (a * a) % m;
        b >>= 1;
    }
    return res;
}

///////////////////////////////////////Working Area///////////////////////////////////////

void solve()
{
    // Check Constrains. Do you need to take long long insteed of int?
    // Go and check Bold statements

    int n;
    cin >> n;

    string a, b;
    cin >> a >> b;

    ll equal = 1, less = 1, greater = 1;
    ll cnt = 0;

    for (int i = 0; i < n; i++)
    {
        if (a[i] == '?' && b[i] == '?')
        {
            cnt += 2;

            equal = (equal * 10) % mod;
            greater = (greater * 55) % mod;
            less = (less * 55) % mod;
        }
        else if (a[i] == '?')
        {
            cnt++;
            int y = b[i] - '0';
            greater = (greater * (10 - y)) % mod;
            less = (less * (y + 1)) % mod;
        }
        else if (b[i] == '?')
        {
            cnt++;
            int x = a[i] - '0';

            greater = (greater * (x + 1)) % mod;
            less = (less * (10 - x)) % mod;
        }
        else
        {
            int x = a[i] - '0', y = b[i] - '0';

            if (x > y)
            {
                equal = 0;
                less = 0;
            }
            else if (x < y)
            {
                equal = 0;
                greater = 0;
            }
        }
    }

    cout << (power(10, cnt, mod) + equal - less - greater + 3 * mod) % mod << endl;
}

////////////////////////////////////////////////////////////////////////////////////////
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);

    // int t;
    // cin >> t;

    // for (int i = 0; i < t; i++)
    solve();

    return 0;
}