Finished day 5

05/example

@@ -0,0 +1,28 @@
+47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47

05/main.cc

@@ -0,0 +1,133 @@
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <vector>
+#include <map>
+#include <set>
+using namespace std;
+
+// constraints maps n to all values that need to appear after n
+bool checkUpdate(vector<int> update, map<int, set<int, greater<int>>> constraints) {
+  // holds all values that have been visited already in this update
+  vector<int> prev;
+
+  for (auto n : update) {
+    for (auto p : prev) {
+      if (constraints[n].count(p)) {
+        return false;
+      }
+    }
+    prev.push_back(n);
+  }
+
+  return true;
+}
+
+// parse constraints, aka lines of integer tuples separated by "|"
+void parseConstraints(ifstream &input, map<int, set<int, greater<int>>> &constraints) {
+  string line;
+  while (getline(input, line) && line.size()) {
+    stringstream line_stream;
+    line_stream << line;
+
+    int a;
+    int b;
+    char c;
+
+    line_stream >> a;
+    // discard "|"
+    line_stream >> c;
+    line_stream >> b;
+
+    // add b to constraint set of a
+    if (constraints.count(a) == 0) {
+      set<int, greater<int>> constraint{b};
+      constraints.insert({a, constraint});
+    } else {
+      constraints[a].insert(b);
+    }
+  }
+}
+
+// parse updates, aka lines of comma separated values
+void parseUpdates(ifstream &input, vector<vector<int>> &updates) {
+  string line;
+  while (getline(input, line)) {
+    // cout << "parseUpdates got line: " << line << endl;
+    int n;
+    stringstream line_stream;
+    line_stream << line;
+    vector<int> v;
+    while (line_stream >> n) {
+      v.push_back(n);
+      char c;
+      // discard comma
+      line_stream >> c;
+    }
+    updates.push_back(v);
+  }
+}
+
+// sums up the middle values of correct updates
+int correctUpdates(map<int, set<int, greater<int>>> constraints, vector<vector<int>> updates) {
+  int sum = 0;
+  for (auto update : updates) {
+    if (checkUpdate(update, constraints)) {
+      sum += update[update.size() / 2];
+    }
+  }
+  return sum;
+}
+
+// corrects an incorrect update by doing something akin to bubble sort 
+// (aka swapping rule violating pairs until there are none left)
+void correction(vector<int> &update, map<int, set<int, greater<int>>> constraints) {
+  for (int i = 0; i < update.size(); i++) {
+    for (int j = 0; j < i; j++) {
+      if (constraints[update[i]].count(update[j])) {
+        // swap n and p, then start over
+        int temp = update[i];
+        update[i] = update[j];
+        update[j] = temp;
+        correction(update, constraints);
+        return;
+      }
+    }
+  }
+}
+
+// sums up the middle values of incorrect updates after correcting them
+int incorrectUpdates(map<int, set<int, greater<int>>> constraints, vector<vector<int>> updates) {
+  int sum = 0;
+  for (auto update : updates) {
+    if (!checkUpdate(update, constraints)) {
+      correction(update, constraints);
+      sum += update[update.size() / 2];
+    }
+  }
+
+  return sum;
+}
+
+int main(int argc, char *argv[]) {
+  ifstream example("example");
+  ifstream input("input");
+
+  map<int, set<int, greater<int>>> constraints_example;
+  vector<vector<int>> updates_example;
+  parseConstraints(example, constraints_example);
+  parseUpdates(example, updates_example);
+
+  cout << "Update sum (example) is: " << correctUpdates(constraints_example, updates_example) << endl;
+  cout << "Corrected update sum (example) is: " << incorrectUpdates(constraints_example, updates_example) << endl;
+
+  map<int, set<int, greater<int>>> constraints_input;
+  vector<vector<int>> updates_input;
+  parseConstraints(input, constraints_input);
+  parseUpdates(input, updates_input);
+
+  cout << "Update sum (input) is: " << correctUpdates(constraints_input, updates_input) << endl;
+  cout << "Corrected update sum (input) is: " << incorrectUpdates(constraints_input, updates_input) << endl;
+
+  return 0;
+}