Added older advents

advent_of_code_2018/day12/main.cc

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+#include <algorithm>
+#include <iomanip>
+#include <iostream>
+#include <string>
+#include <vector>
+#include <unordered_map>
+
+using namespace std;
+
+unordered_map<string, char> read_rules()
+{
+    unordered_map<string, char> rules;
+
+    while(!cin.eof())
+    {
+        char result;
+        string rule;
+
+        cin >> rule;
+        cin.ignore(4); //ignore ' => '
+        cin >> result;
+        cin.ignore(1); //ignore '\n'
+
+        rules[rule] = result;
+    }
+
+    return rules;
+}
+
+vector<char> initial_state()
+{
+    cin.ignore(15); // ignore 'initial state: '
+    string buf;
+    getline(cin, buf);
+
+    return vector<char>(buf.begin(), buf.end());
+}
+
+string environment(vector<char> const &plants, size_t idx)
+{
+    string sig;
+    
+    switch(idx)
+    {
+        case 0:
+            sig += "..";
+            sig += string(plants.begin(), plants.begin() + 3);
+            return sig;
+        
+        case 1:
+
+            sig += ".";
+            sig += string(plants.begin(), plants.begin() + 4);
+            return sig;
+
+        default:
+        break;
+    }
+
+    if (idx == (plants.size() - 2))
+    {
+        auto it = plants.begin() + idx;
+        return string(it - 2, it + 2) + '.';
+    }
+    else if (idx == (plants.size() - 1))
+    {
+        auto it = plants.begin() + idx;
+        return string(it - 2, it + 1) + "..";
+    }
+
+    auto it = plants.begin() + idx;
+    return string(it - 2, it + 3);
+}
+
+int main()
+{
+    int first = 0;
+    vector<char> plants = initial_state();
+    unordered_map<string, char> rules = read_rules();
+
+    string original = string(plants.begin(), plants.end());
+    cout << original << "\n";
+
+    for (size_t iterations = 20; iterations--; )
+    {
+        if (find(plants.begin(), plants.begin() + 3, '#')
+             != plants.begin() + 3)
+        {
+            first -= 2;
+            plants.insert(plants.begin(), {'.', '.'});
+        }
+
+        if (find(plants.end() - 3, plants.end(), '#')
+            != plants.end())
+        {
+            plants.insert(plants.end(), {'.', '.'});
+        }
+        vector<char> nextgen(plants.size(), '.');
+
+        // cout << "\n\n  # now   env    new\n";
+        for (size_t idx = 0; idx != plants.size(); ++idx)
+        {
+            // cout << setw(3) << first + static_cast<int>(idx) << " ";
+            // cout << "[" << plants[idx] << "]: ";
+            string env = environment(plants, idx);
+            // cout << env << " => ";
+
+            char result = '?';
+            if (auto it = rules.find(env); it != rules.end())
+                result = it->second;
+            // cout << result << "\n";
+            nextgen[idx] = result;
+        }
+        plants.swap(nextgen);
+    }
+
+    // cout << string(-first, ' ') << original << "\n";
+    // cout << string(plants.begin(), plants.end()) << "\n";
+
+    int score = 0;
+    for (size_t idx = 0; idx < plants.size(); ++idx)
+    {
+        score += (plants[idx] == '#' ? idx + first : 0);
+    }
+    cout << "score: " << score << "\n";
+    
+}