From 46b2ae6ef0980ed3e1f55257fc6918cfcfd39cae Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Mon, 23 Dec 2019 18:36:48 +0100
Subject: [PATCH] Implement starting point for day 10.

---
 2019/src/day20.cpp | 113 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 111 insertions(+), 2 deletions(-)

diff --git a/2019/src/day20.cpp b/2019/src/day20.cpp
index bb8a3a7..3bc489c 100644
--- a/2019/src/day20.cpp
+++ b/2019/src/day20.cpp
@@ -1,10 +1,119 @@
 #include <iostream>
+#include <vector>
+#include <map>
+#include <unordered_set>
+#include <queue>
 #include "days.hpp"
+#include "point.hpp"
+
+namespace {
+    typedef aoc2019::Point<int, 2> point_t;
+    typedef std::vector<std::string> map_t;
+
+    std::array<point_t, 4> DIRECTIONS = {{
+                                                 {0, -1},
+                                                 {0, 1},
+                                                 {-1, 0},
+                                                 {1, 0},
+                                         }};
+
+    std::vector<std::string> read_map(std::istream &input) {
+        std::string buffer;
+        std::vector<std::string> map;
+
+        while (std::getline(input, buffer)) {
+            map.push_back(buffer);
+        }
+
+        return map;
+    }
+
+    std::pair<std::unordered_map<std::string, point_t>, std::unordered_map<std::string, std::pair<point_t, point_t>>>
+    get_portals(const map_t &map) {
+        std::unordered_map<std::string, point_t> half_portals;
+        std::unordered_map<std::string, std::pair<point_t, point_t>> portals;
+
+        // First find horizontal portals
+        for (int y = 0; y < map.size(); ++y) {
+            for (int x = 0; x < map[y].size() - 1; ++x) {
+                if (std::isalpha(map[y][x]) && std::isalpha(map[y][x + 1])) {
+                    // find out the entry point
+                    point_t entry_point = {0, y};
+                    if (x > 0 && map[y][x - 1] == '.') {
+                        entry_point[0] = x;
+                    } else {
+                        entry_point[0] = x + 1;
+                    }
+
+                    auto name = map[y].substr(x, 2);
+
+                    if (auto it = half_portals.find(name); it != half_portals.end()) {
+                        portals[name] = {entry_point, it->second};
+                    } else {
+                        half_portals[name] = entry_point;
+                    }
+                }
+            }
+        }
+
+        char name[3] = {0, 0, 0};
+        for (int x = 0; x < map[0].size(); ++x) {
+            for (int y = 0; y < map.size() - 1; ++y) {
+                if (std::isalpha(map[y][x]) && std::isalpha(map[y + 1][x])) {
+                    name[0] = map[y][x];
+                    name[1] = map[y + 1][x];
+
+                    point_t entry_point = {x, 0};
+                    if (y > 0 && map[y - 1][x] == '.') {
+                        entry_point[1] = y;
+                    } else {
+                        entry_point[1] = y + 1;
+                    }
+
+                    if (auto it = half_portals.find(name); it != half_portals.end()) {
+                        portals[name] = {entry_point, it->second};
+                    } else {
+                        half_portals[name] = entry_point;
+                    }
+                }
+            }
+        }
+
+        return std::make_pair(half_portals, portals);
+    }
+}
 
 void aoc2019::day20_part1(std::istream &input, std::ostream &output) {
-	output << "Not implemented\n";
+    const auto map = read_map(input);
+    auto[half_portals, portals] = get_portals(map);
+
+    const auto starting_point = half_portals.at("AA");
+    const auto goal = half_portals.at("ZZ");
+
+    std::unordered_map<point_t, point_t> links;
+    for (auto &link : portals) {
+        links[link.second.first] = link.second.second;
+        links[link.second.second] = link.second.first;
+    }
+
+    std::unordered_set<point_t> visited{starting_point};
+    std::queue<std::pair<int, point_t>> todo;
+    todo.emplace(0, starting_point);
+
+    while (!todo.empty()) {
+        const auto[dist, pos] = todo.front();
+        todo.pop();
+
+        if (pos == goal) {
+            output << dist << std::endl;
+            return;
+        }
+
+    }
+
+    output << "Not implemented\n";
 }
 
 void aoc2019::day20_part2(std::istream &input, std::ostream &output) {
-	output << "Not implemented\n";
+    output << "Not implemented\n";
 }