From 10100da5e97a7dac3d97f3175fbddc26997ca79d Mon Sep 17 00:00:00 2001
From: Leon Vatthauer <leon.vatthauer@fau.de>
Date: Wed, 11 Dec 2024 16:57:08 +0100
Subject: [PATCH] solve day 10

---
 10/example |   8 ++++
 10/input   |  53 ++++++++++++++++++++
 10/main.cc | 138 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 199 insertions(+)
 create mode 100644 10/example
 create mode 100644 10/input
 create mode 100644 10/main.cc

diff --git a/10/example b/10/example
new file mode 100644
index 0000000..cada9b3
--- /dev/null
+++ b/10/example
@@ -0,0 +1,8 @@
+89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732
diff --git a/10/input b/10/input
new file mode 100644
index 0000000..d454397
--- /dev/null
+++ b/10/input
@@ -0,0 +1,53 @@
+65456780121098450187634569763232345103213014321223456
+56565097632787543296323478890141234234102125630310767
+67874198545601612345610165765650105145693496543407898
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diff --git a/10/main.cc b/10/main.cc
new file mode 100644
index 0000000..df40665
--- /dev/null
+++ b/10/main.cc
@@ -0,0 +1,138 @@
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <vector>
+#include <tuple>
+#include <set>
+
+using namespace std;
+
+vector<vector<int>> parseGrid(const char *path) {
+  vector<vector<int>> grid;
+
+  ifstream input(path);
+  string line;
+  while (getline(input, line)) {
+    char c;
+    vector<int> row;
+    stringstream ss;
+    ss << line;
+    while (ss >> c) {
+      int num = c - '0';
+      row.push_back(num);
+    }
+    grid.push_back(row);
+  }
+  return grid;
+}
+
+void printGrid(vector<vector<int>> grid) {
+  for (int y = 0; y < grid.size(); y++) {
+    for (int x = 0; x < grid[0].size(); x++) {
+      cout << grid[y][x];
+    }
+    cout << endl;
+  }
+}
+
+int trailheadHelper(vector<vector<int>> grid, int y, int x, set<tuple<int,int>, greater<tuple<int,int>>> &visited) {
+  int curr = grid[y][x];
+
+  // base case
+  if (curr == 9) {
+    if (visited.count(make_tuple(y,x))) {
+      return 0;
+    } else {
+      visited.insert(make_tuple(y,x));
+      return 1;
+    }
+  }
+
+  int sum = 0;
+
+  // try each direction
+  if (x > 0 && grid[y][x - 1] == grid[y][x] + 1) {
+    sum += trailheadHelper(grid, y, x - 1, visited);
+  }
+  if (x < grid[y].size() - 1 && grid[y][x + 1] == grid[y][x] + 1) {
+    sum += trailheadHelper(grid, y, x + 1, visited);
+  }
+  if (y > 0 && grid[y - 1][x] == grid[y][x] + 1) {
+    sum += trailheadHelper(grid, y - 1, x, visited);
+  }
+  if (y < grid.size() - 1 && grid[y + 1][x] == grid[y][x] + 1) {
+    sum += trailheadHelper(grid, y + 1, x, visited);
+  }
+
+  return sum;
+}
+
+int trailheadCount(vector<vector<int>> grid, int y, int x) {
+  set<tuple<int,int>, greater<tuple<int,int>>> visited;
+
+  return trailheadHelper(grid, y, x, visited);
+}
+
+int trailheadCount2(vector<vector<int>> grid, int y, int x) {
+  int curr = grid[y][x];
+
+  // base case
+  if (curr == 9) {
+    return 1;
+  }
+
+  int sum = 0;
+
+  // try each direction
+  if (x > 0 && grid[y][x - 1] == grid[y][x] + 1) {
+    sum += trailheadCount2(grid, y, x - 1);
+  }
+  if (x < grid[y].size() - 1 && grid[y][x + 1] == grid[y][x] + 1) {
+    sum += trailheadCount2(grid, y, x + 1);
+  }
+  if (y > 0 && grid[y - 1][x] == grid[y][x] + 1) {
+    sum += trailheadCount2(grid, y - 1, x);
+  }
+  if (y < grid.size() - 1 && grid[y + 1][x] == grid[y][x] + 1) {
+    sum += trailheadCount2(grid, y + 1, x);
+  }
+
+  return sum;
+}
+
+
+int part1(const char *path) {
+  vector<vector<int>> grid = parseGrid(path);
+
+  int sum = 0;
+  for (int y = 0; y < grid.size(); y++) {
+    for (int x = 0; x < grid[0].size(); x++) {
+      if (grid[y][x] == 0) {
+        sum += trailheadCount(grid, y, x);
+      }
+    }
+  }
+  return sum;
+}
+
+int part2(const char *path) {
+  vector<vector<int>> grid = parseGrid(path);
+
+  int sum = 0;
+  for (int y = 0; y < grid.size(); y++) {
+    for (int x = 0; x < grid[0].size(); x++) {
+      if (grid[y][x] == 0) {
+        sum += trailheadCount2(grid, y, x);
+      }
+    }
+  }
+  return sum;
+}
+
+int main(int argc, char *argv[]) {
+  cout << "example1: " << part1("example") << endl;
+  cout << "input1: " << part1("input") << endl;
+  cout << "example2: " << part2("example") << endl;
+  cout << "input2: " << part2("input") << endl;
+  return 0;
+}