Maximum Product

#include <bits/stdc++.h>
using ll = long long;
using namespace std;
 
/** @return the product of the given string's digits (-1 if empty) */
ll prod(string s) {
	// remove leading zeros
	int i = 0;
	while (s[i] == '0') { i++; }
	s = s.substr(i);
 
	if (!s.length()) { return -1; }
	ll res = 1;
	for (char c : s) { res *= c - '0'; }
	return res;
}
 
int main() {
	string l, r;
	cin >> l >> r;
 
	// pad beginning of l with zeros
	// l = 12, r = 132 -> l = 012, r = 132
	while (l.length() < r.length()) { l.insert(l.begin(), '0'); }
	string ans = "";
 
	// i -> length of LCP (longest common prefix) of str and r
	bool eq = true;  // whether l[0, i) = r[0, i)
	for (int i = 0; i <= r.length(); i++) {
		string cur = r.substr(0, i);
		eq = eq && l[i] == r[i];
		/*
		 * in this case, str[i] must equal r[i]
		 * and now the shared prefix has length i + 1
		 * which contradicts our assumption that the LCP has length i
		 */
		if (i < r.length() && eq) { continue; }
		if (i < r.length()) { cur += char(r[i] - 1); }
		// fill remaining digits with 9's
		cur += string(r.length() - cur.length(), '9');
		if (prod(cur) > prod(ans)) { ans = cur; }
	}
 
	// remove any leading zeros from ans
	while (ans[0] == '0') { ans.erase(ans.begin()); }
	cout << ans << endl;
}