Maximum Product

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

typedef int64_t i64;

int sz;
i64 a, b;
i64 ans, maxAns;
string lo, hi;

pair<i64, string> dp[19][2][2][2];
bool calc[19][2][2][2];

pair<i64, string> solve(int idx, bool st, bool canLo, bool canHi, i64 val) {
  if (idx == sz) return {1LL, ""};

  if (calc[idx][st][canLo][canHi])
    return dp[idx][st][canLo][canHi];

  pair<i64, string> ans = {-1, ""};
  int l = canLo ? 0 : lo[idx] - '0';
  int r = canHi ? 9 : hi[idx] - '0';
  for (int i = l; i <= r; ++i) {
    bool hasStarted = st | (i != 0);
    auto res = solve(idx + 1, hasStarted, canLo | (l < i), canHi | (i < r), val * (hasStarted ? i : 1));
    ans = max(ans, {(hasStarted ? i : 1) * res.first, to_string(i) + res.second});
  }

  calc[idx][st][canLo][canHi] = true;
  return dp[idx][st][canLo][canHi] = ans;
}

int main() {
  cin.tie(0)->sync_with_stdio(0);

  cin >> a >> b;

  lo = to_string(a);
  hi = to_string(b);

  sz = max(lo.size(), hi.size());

  while (lo.size() < sz) lo = '0' + lo;
  while (hi.size() < sz) hi = '0' + hi;

  string ans = solve(0, 0, 0, 0, 1).second;

  int cnt = 0;
  while (ans[cnt] == '0') ++cnt;

  cout << ans.substr(cnt) << '\n';
}