Solve 2024 day 5 part 1

2024/day-05/main.cpp

@@ -0,0 +1,125 @@
+#include <algorithm>
+#include <iostream>
+#include <sstream>
+#include <vector>
+
+using namespace std;
+
+vector<pair<int, int>> readRules()
+{
+    vector<pair<int, int>> rules;
+    string line;
+    while (getline(cin, line)) {
+        if (line == "") {
+            break;
+        }
+        int number1 = stoi(line.substr(0, 2));
+        int number2 = stoi(line.substr(3, 2));
+        rules.push_back(make_pair(number1, number2));
+    }
+    return rules;
+}
+
+vector<vector<int>> readManuals()
+{
+    vector<vector<int>> manuals;
+    string line;
+    while (getline(cin, line)) {
+        manuals.push_back({});
+        stringstream inStream(line);
+        string page;
+        while (getline(inStream, page, ',')) {
+            manuals.back().push_back(stoi(page));
+        }
+    }
+    return manuals;
+}
+
+vector<pair<int, int>> getSortedLessThanRules(vector<pair<int, int>> rules)
+{
+    sort(rules.begin(), rules.end(), [](auto a, auto b) { return a.first < b.first; });
+    return rules;
+}
+
+vector<pair<int, int>> getSortedGreaterThanRules(vector<pair<int, int>> rules)
+{
+    for (pair<int, int> &rule : rules) {
+        swap(rule.first, rule.second);
+    }
+    sort(rules.begin(), rules.end(), [](auto a, auto b) { return a.first < b.first; });
+    return rules;
+}
+
+enum class Comparison { lessThan, greaterThan };
+
+bool pageIsFollowingRules(const vector<int> &pages,
+                          const size_t indexOfPageToCheck,
+                          const vector<pair<int, int>> &rules,
+                          const Comparison ruleType)
+{
+    size_t indexOfFirstRule = lower_bound(rules.begin(),
+                                          rules.end(),
+                                          pages[indexOfPageToCheck],
+                                          [](pair<int, int> a, int b) { return a.first < b; })
+                              - rules.begin();
+
+    if (indexOfFirstRule == rules.size()) {
+        return true;
+    }
+
+    size_t pagesStart, pagesEnd;
+    if (ruleType == Comparison::lessThan) {
+        pagesStart = 0;
+        pagesEnd = indexOfPageToCheck;
+    } else {
+        pagesStart = indexOfPageToCheck;
+        pagesEnd = pages.size();
+    }
+
+    for (size_t pageIndex = pagesStart; pageIndex < pagesEnd; pageIndex++) {
+        for (size_t ruleIndex = indexOfFirstRule;
+             ruleIndex < rules.size() && rules[ruleIndex].first == pages[indexOfPageToCheck];
+             ruleIndex++) {
+            if (pages[pageIndex] == rules[ruleIndex].second) {
+                return false;
+            }
+        }
+    }
+
+    return true;
+}
+
+int getMiddlePageNumber(vector<int> pages)
+{
+    size_t middleIndex = pages.size() / 2;
+    return pages[middleIndex];
+}
+
+int main()
+{
+    vector<pair<int, int>> unsortedRules = readRules();
+    vector<vector<int>> manuals = readManuals();
+
+    vector<pair<int, int>> lessThanRules = getSortedLessThanRules(unsortedRules);
+    vector<pair<int, int>> greaterThanRules = getSortedGreaterThanRules(unsortedRules);
+
+    int middlePageNumberSum = 0;
+
+    for (const vector<int> &pages : manuals) {
+        bool correctlyOrdered = true;
+        for (size_t i = 0; i < pages.size(); i++) {
+            if (!pageIsFollowingRules(pages, i, lessThanRules, Comparison::lessThan)
+                || !pageIsFollowingRules(pages, i, greaterThanRules, Comparison::greaterThan)) {
+                correctlyOrdered = false;
+                break;
+            }
+        }
+        if (correctlyOrdered) {
+            middlePageNumberSum += getMiddlePageNumber(pages);
+        }
+    }
+
+    // Part one
+    cout << "Sum of the middle page numbers of all correctly ordered manuals: "
+         << middlePageNumberSum << endl;
+}