From 7b6cadffc8f92a1e63183181403f9d09fbdf09d0 Mon Sep 17 00:00:00 2001
From: Felix Agner <felix.agner@control.lth.se>
Date: Wed, 18 Dec 2024 08:06:12 +0100
Subject: [PATCH] gotta avoid those falling bytes.
---
day 18/day_18_felix.cpp | 114 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 114 insertions(+)
create mode 100644 day 18/day_18_felix.cpp
diff --git a/day 18/day_18_felix.cpp b/day 18/day_18_felix.cpp
new file mode 100644
index 0000000..c739273
--- /dev/null
+++ b/day 18/day_18_felix.cpp
@@ -0,0 +1,114 @@
+#include <bits/stdc++.h>
+using namespace std;
+const bool DEBUG = false;
+
+#define coord pair <int, int>
+#define ll long long
+
+const coord START = {0, 0};
+vector<array<array<bool,71>,71>> UNSAFE;
+const coord GOAL = DEBUG ? coord(6, 6) : coord(70, 70);
+int N_STEP = DEBUG ? 11 : 1023;
+vector<coord> obstacles;
+
+void parse_input() {
+ string line;
+ int row = 0;
+ int x, y;
+ char comma;
+ array<array<bool,71>,71> unsafe = {false};
+ while (getline(cin, line)) {
+ stringstream ss(line);
+ ss >> x >> comma >> y;
+ cout << x << " " << y << endl;
+ unsafe[x][y] = true;
+ UNSAFE.push_back(unsafe);
+ obstacles.push_back({x, y});
+ }
+}
+
+bool out_of_bounds(coord c) {
+ return c.first < 0 || c.first > GOAL.first || c.second < 0 || c.second > GOAL.second;
+}
+
+vector<coord> neighbors(coord c) {
+ return {
+ {c.first + 1, c.second},
+ {c.first - 1, c.second},
+ {c.first, c.second + 1},
+ {c.first, c.second - 1}
+ };
+}
+
+ll dijkstra(int step) {
+ map<coord, ll> costs;
+ ll best_cost = LLONG_MAX;
+ costs[START] = 0;
+
+ auto cost_comp = [&costs](const coord& lhs, const coord& rhs) {
+ return costs[lhs] > costs[rhs];
+ };
+
+ priority_queue<coord, vector<coord>, decltype(cost_comp)> q(cost_comp);
+ q.push(START);
+
+ while (!q.empty()) {
+ coord cur = q.top();
+ q.pop();
+
+ if (out_of_bounds(cur)) continue;
+
+ if (cur == GOAL){
+ best_cost = costs[cur];
+ break;
+ }
+
+ for (auto n : neighbors(cur)) if (!out_of_bounds(n)) {
+ if (UNSAFE[step][n.first][n.second]) continue;
+ ll new_cost = costs[cur] + 1;
+ if (!costs.count(n) || costs[n] > new_cost) {
+ costs[n] = new_cost;
+ q.push(n);
+ }
+ }
+ }
+ // for (auto c : costs) {
+ // cout << c.first.first << " " << c.first.second << " cost: " << c.second << endl;
+ // }
+
+ return best_cost;
+}
+
+void visualize(int step) {
+ vector<string> grid(GOAL.first + 1, string(GOAL.second + 1, '.'));
+ for (int x = 0; x <= GOAL.first; x++) {
+ for (int y = 0; y <= GOAL.second; y++) {
+ if (UNSAFE[step][x][y]) grid[y][x] = '#';
+ }
+ }
+ for (int row = 0; row <= GOAL.first; row++) {
+ cout << grid[row] << endl;
+ }
+}
+
+int main () {
+ parse_input();
+ visualize(N_STEP);
+ cout << "Part 1: " << dijkstra(N_STEP) << endl;
+
+ int upper = UNSAFE.size();
+ int lower = N_STEP;
+ int guess = (upper + lower) / 2;
+ while (upper - lower > 1) {
+ if (dijkstra(guess) == LLONG_MAX) {
+ upper = guess;
+ } else {
+ lower = guess;
+ }
+ guess = (upper + lower) / 2;
+ }
+ cout << "Lower: " << lower << " " << obstacles[lower].first << ", " << obstacles[lower].second << endl;
+ cout << "Upper: " << upper << " " << obstacles[upper].first << ", " << obstacles[upper].second << endl;
+
+ return 0;
+}
\ No newline at end of file
--
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