Day 10

d10/main.cxx

@@ -1,15 +1,130 @@
+#include <utility>
+#include <vector>
+#include <string>
+#include <sstream>
+#include <unordered_set>
+#include <chrono>
 #include <iostream>
-#include <fstream>
 
 using std::cout, std::endl;
 
-int main() {
+constexpr const char content[] = {
-    std::ifstream file{"../d10/input.txt"};
+    #embed "input.txt"
-    std::string line;
+};
 
-    while (std::getline(file, line)) {
+using Position = std::pair<int, int>;
-        
+
+bool operator==(const Position& lhs, const Position& rhs) {
+    return lhs.first == rhs.first && lhs.second == rhs.second;
+}
+
+namespace std {
+    template <>
+    struct hash<Position> {
+        std::size_t operator()(const Position& p) const {
+            return std::hash<int>{}(p.first) ^ std::hash<int>{}(p.second);
+        }
+    };
+}
+
+int path_count(std::vector<std::string>& grid, Position p, std::unordered_set<Position>& seen) {
+    constexpr auto target = '9';
+
+    if (seen.contains(p)) {
+        return 0;
+    } else {
+        seen.insert(p);
     }
+
+    if (grid[p.first][p.second] == target) {
+        return 1;
+    }
+
+    int paths = 0;
+    for(auto [i, j] : {std::pair{0, 1}, {0, -1}, {1, 0}, {-1, 0}}) {
+        const int nexti = p.first + i;
+        const int nextj = p.second + j;
+        if (nexti < 0 || nexti >= grid.size() || nextj < 0 || nextj >= grid[nexti].size()) {
+            continue;
+        }
+        if (grid[nexti][nextj] == grid[p.first][p.second] + 1) {
+            paths += path_count(grid, {nexti, nextj}, seen);
+        }
+    }
+
+    return paths;
+}
+
+int part_1() {
+    std::istringstream input_stream(content);
+    std::string line;
+    std::vector<std::string> grid = {};
+    while(std::getline(input_stream, line)) {
+        grid.push_back(line);
+    }
+
+    int tailheads = 0;
+    for(int i = 0; i < grid.size(); ++i) {
+        for(int j = 0; j < grid[i].size(); ++j) {
+            if (grid[i][j] == '0') {
+                std::unordered_set<Position> seen;
+                tailheads += path_count(grid, {i, j}, seen);
+            }
+        }
+    }
+
+    return tailheads;
+}
+
+int all_path_count(std::vector<std::string>& grid, Position p) {
+    constexpr auto target = '9';
     
+    if (grid[p.first][p.second] == target) {
+        return 1;
+    }
+
+    int paths = 0;
+    for(auto [i, j] : {std::pair{0, 1}, {0, -1}, {1, 0}, {-1, 0}}) {
+        const int nexti = p.first + i;
+        const int nextj = p.second + j;
+        if (nexti < 0 || nexti >= grid.size() || nextj < 0 || nextj >= grid[nexti].size()) {
+            continue;
+        }
+        if (grid[nexti][nextj] == grid[p.first][p.second] + 1) {
+            paths += all_path_count(grid, {nexti, nextj});
+        }
+    }
+
+    return paths;
+}
+
+int part_2() {
+    std::istringstream input_stream(content);
+    std::string line;
+    std::vector<std::string> grid = {};
+    while(std::getline(input_stream, line)) {
+        grid.push_back(line);
+    }
+
+    int tailheads = 0;
+    for(int i = 0; i < grid.size(); ++i) {
+        for(int j = 0; j < grid[i].size(); ++j) {
+            if (grid[i][j] == '0') {
+                tailheads += all_path_count(grid, {i, j});
+            }
+        }
+    }
+
+    return tailheads;
+}
+
+int main() {
+    std::chrono::steady_clock::time_point begin = std::chrono::steady_clock::now();
+    auto p1_val = part_1();
+    std::chrono::steady_clock::time_point middle = std::chrono::steady_clock::now();
+    auto p2_val = part_2();
+    std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();
+    cout << "Part 1: " << p1_val << " (" << std::chrono::duration_cast<std::chrono::microseconds>(middle - begin).count() << "µs)" << endl;  
+    cout << "Part 2: " << p2_val << " (" << std::chrono::duration_cast<std::chrono::microseconds>(end - middle).count() << "µs)" << endl;
     return 0;
 }