advent-of-code/2023/3/main-2.cpp

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

inline bool isDigit(char ch) {
	return ch >= '0' && ch <= '9';
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	vector<string> lines;
	string line;
	while (getline(cin, line) && !line.empty()) {
		lines.push_back(line);
	}

	int ret = 0;

	for (int r = 0; r < lines.size(); r++) {
		auto& line = lines[r];
		int cend = line.size();
		for (int c = 0; c < cend; c++) {
			char ch = line[c];
			if (ch != '*')
				continue;
			vector<int> rs = {r}, cs = {c};
			int p = 1;
			int n = 0;
			for (int rr = r - 1; rr <= r + 1; rr++) {
				if (rr < 0 || rr == lines.size())
					continue;
				for (int cc = c - 1; cc <= c + 1; cc++) {
					if (cc < 0 || cc == cend)
						continue;
					auto& lo = lines[rr];
					if (isDigit(lo[cc])) {
						int ci = cc, cf = cc;
						while (ci > 0 && isDigit(lo[ci - 1]))
							ci--;
						while (cf < cend - 1 && isDigit(lo[cf + 1]))
							cf++;
						p *= stoi(lo.substr(ci, cf - ci + 1));
						for (int i = ci; i <= cf; i++)
							lo[i] = '.';
						if (++n > 2)
							goto rrccend;
					}
				}
			}
		rrccend:
			if (n == 2)
				ret += p;
		}
	}

	cout << ret << '\n';
}