Added older advents

advent_of_code_2018/day7/main1.cc

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+#include <algorithm>
+#include <array>
+#include <iostream>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+struct Constraint
+{
+    bool placed = false;
+    vector<char> requires;
+    vector<char> required_by;
+};
+
+bool satisfied(Constraint const &constraint, string const &plan)
+{
+    for (char c : constraint.requires)
+    {
+        if (plan.find(c) == string::npos)
+            return false;
+    }
+    return true;
+}
+
+int main()
+{
+    array<Constraint, 26> constraints {};
+
+    while (!cin.eof())
+    {
+        char step;
+        char requires;
+
+        cin.ignore(5); // 'Step '
+        cin >> requires;
+        cin.ignore(30); // ' must be finished before step '
+        cin >> step;
+        cin.ignore(12); //' can begin.\n'
+
+        cout << step << " requires " << requires << "\n";
+        constraints[step - 'A'].requires.push_back(requires);
+        constraints[requires - 'A'].required_by.push_back(step);
+    }
+
+    string plan;
+    while(plan.size() != 26)
+    {
+        for (size_t idx = 0; idx < 26; ++idx)
+        {
+            if (!constraints[idx].placed && satisfied(constraints[idx], plan))
+            {
+                plan += static_cast<char>('A' + idx);
+                constraints[idx].placed = true;
+                break;
+            }
+        }
+
+        cout << plan.size() << " / '" << plan << "'\n";
+    }
+
+    cout << plan.size() << " / '" << plan << "'\n";
+}