From ec95deb6f565d7994876932834489e7a22e19e11 Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano@tronto.net>
Date: Fri, 13 Dec 2024 10:28:14 +0100
Subject: Day 12 2024, cleaned up part b

---
 2024/12/day12a.cpp | 149 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 149 insertions(+)
 create mode 100644 2024/12/day12a.cpp

(limited to '2024/12/day12a.cpp')

diff --git a/2024/12/day12a.cpp b/2024/12/day12a.cpp
new file mode 100644
index 0000000..b972fd2
--- /dev/null
+++ b/2024/12/day12a.cpp
@@ -0,0 +1,149 @@
+/*
+This code is a bit ugly, day12b.cpp contains a nicer implementation
+(the perimeter part is of course different).
+*/
+
+#include <iostream>
+#include <algorithm>
+#include <string>
+#include <string_view>
+#include <vector>
+using namespace std;
+
+enum class Direction { U, D, R, L };
+Direction all_directions[] = {
+	Direction::U, Direction::D, Direction::R, Direction::L,
+};
+
+pair<int, int> step(pair<int, int> p, Direction d) {
+	auto [i, j] = p;
+
+	switch (d) {
+	case Direction::U:
+		return make_pair(i-1, j);
+	case Direction::D:
+		return make_pair(i+1, j);
+	case Direction::R:
+		return make_pair(i, j+1);
+	case Direction::L:
+		return make_pair(i, j-1);
+	}
+
+	return make_pair(-999,-999);
+}
+
+class Board {
+public:
+	const char out_of_bound = '$';
+	int M, N;
+
+	Board(vector<string> &lines) {
+		N = lines.size();
+		M = 0;
+		for (string l : lines)
+			M = max(M, (int)l.size());
+		region = new int[M * N];
+		cells = new char[M * N];
+		for (int i = 0; i < N; i++) {
+			for (int j = 0; j < M; j++) {
+				region[N*i + j] = -1;
+				cells[N*i + j] = j < (int)lines[i].size() ?
+				    lines[i][j] : out_of_bound;
+			}
+		}
+				
+	}
+
+	~Board() {
+		delete []region;
+		delete []cells;
+	}
+
+	char operator[](pair<int, int> p) {
+		int c = coord(p);
+		return c == -1 ? out_of_bound : cells[c];
+	}
+
+	int& reg(pair<int, int> p) {
+		return region[coord(p)];
+	}
+
+private:
+	char *cells;
+	int *region;
+
+	int coord(pair<int, int> p) {
+		auto [i, j] = p;
+		return i >= N || i < 0 || j >= M || j < 0 ? -1 : N*i + j;
+	}
+};
+
+void fill(pair<int, int> p, char a, int r, Board &board) {
+	if (board[p] != a || board.reg(p) == r)
+		return;
+	board.reg(p) = r;
+
+	fill(step(p, Direction::U), a, r, board);
+	fill(step(p, Direction::D), a, r, board);
+	fill(step(p, Direction::R), a, r, board);
+	fill(step(p, Direction::L), a, r, board);
+}
+
+int cell_perim(Board &board, pair<int, int> p) {
+	int perim = 0;
+	if (board[step(p, Direction::U)] != board[p]) perim++;
+	if (board[step(p, Direction::D)] != board[p]) perim++;
+	if (board[step(p, Direction::R)] != board[p]) perim++;
+	if (board[step(p, Direction::L)] != board[p]) perim++;
+	return perim;
+}
+
+int measure_region(Board &board, int r) {
+	int area = 0;
+	int perim = 0;
+	pair<int, int> p;
+	for (p.first = 0; p.first < board.N; p.first++) {
+		for (p.second = 0; p.second < board.M; p.second++) {
+			if (board.reg(p) == r) {
+				area++;
+				perim += cell_perim(board, p);
+			}
+		}
+	}
+
+	return area * perim;
+}
+
+int scan(Board &board, int maxr) {
+	int tot = 0;
+	for (int r = 0; r < maxr; r++)
+		tot += measure_region(board, r);
+
+	return tot;
+}
+
+int main() {
+	string line;
+	vector<string> lines;
+	while (getline(cin, line))
+		lines.push_back(line);
+
+	Board board(lines);
+
+	pair<int, int> p;
+	int r = 0;
+	for (p.first = 0; p.first < board.N; p.first++) {
+		for (p.second = 0; p.second < board.M; p.second++) {
+			if (board.reg(p) == -1) {
+				fill(p, board[p], r, board);
+				r++;
+			}
+		}
+	}
+
+	auto tot = scan(board, r);
+
+	cout << tot << endl;
+
+	return 0;
+}
-- 
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