advent-of-code/2023/10/main-1.cpp

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

vector<string> lines;

#define R(x, y) rets.push_back(make_pair(r + x, c + y))
vector<pair<int, int>> findcons(int r, int c) {
	vector<pair<int, int>> rets;
	switch (lines[r][c]) {
	case '|':
		R(-1, 0);
		R(1, 0);
		break;
	case '-':
		R(0, -1);
		R(0, 1);
		break;
	case 'L':
		R(-1, 0);
		R(0, 1);
		break;
	case 'J':
		R(-1, 0);
		R(0, -1);
		break;
	case '7':
		R(1, 0);
		R(0, -1);
		break;
	case 'F':
		R(1, 0);
		R(0, 1);
		break;
	case 'S':
		for (int rr = -1; rr <= 1; rr++) {
			for (int cc = -1; cc <= 1; cc++) {
				if (rr == 0 && cc == 0)
					continue;
				unsigned int rrr = r + rr, ccc = c + cc;
				if ((int)rrr < 0 || rrr == lines.size() || (int)ccc < 0 || ccc == lines[rrr].size())
					continue;
				for (auto& con : findcons(rrr, ccc)) {
					if (con.first == r && con.second == c) {
						R(rr, cc);
						goto lend;
					}
				}
			}
		}
	lend:
		break;
	}
	return rets;
}
#undef R

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

	string line;

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

	int sr = 0, sc = 0;
	for (unsigned int rr = 0; rr < lines.size(); rr++) {
		for (unsigned int cc = 0; cc < lines[rr].size(); cc++) {
			if (lines[rr][cc] == 'S') {
				sr = rr;
				sc = cc;
				goto lend;
			}
		}
	}
lend:
	const auto& scons = findcons(sr, sc);
	int lr = sr, lc = sc, r = scons[0].first, c = scons[0].second;
	int ret = 1;

	do {
		for (auto& con : findcons(r, c)) {
			if (con.first == lr && con.second == lc)
				continue;
			lr = r;
			lc = c;
			r = con.first;
			c = con.second;
			ret++;
			break;
		}
	} while (r != sr || c != sc);

	cout << ret / 2 << '\n';
}