feat: WIP leetcode/leetcoding_challenge/2025/jan2025/week4/course_schedule_iv.cpp

Author: htbkoo

src/onlinePlatform/leetcode/leetcoding_challenge/2025/jan2025/week4/course_schedule_iv.cpp

@@ -0,0 +1,118 @@
+#include <algorithm>
+#include <vector>
+#include <queue>
+#include <set>
+#include <limits>
+#include <map>
+#include <unordered_set>
+#include <unordered_map>
+#include <iterator>
+#include <sstream>
+#include <iostream> // includes cin to read from stdin and cout to write to stdout
+using namespace std; // since cin and cout are both in namespace std, this saves some text
+
+class Solution {
+public:
+    vector<bool> checkIfPrerequisite(int numCourses, vector<vector<int>>& prerequisites, vector<vector<int>>& queries) {
+        // TODO: validate there are no cycles
+        
+        vector<int> indegrees(numCourses, 0);        
+        vector<unordered_set<int>> nextCourses(numCourses, unordered_set<int>());        
+        vector<unordered_set<int>> allPrerequisites(numCourses, unordered_set<int>());
+        for (auto& prerequisite: prerequisites) {
+            auto first = prerequisite[0];
+            auto after = prerequisite[1];
+            
+            indegrees[after]++;
+            nextCourses[first].insert(after);
+            allPrerequisites[after].insert(first);
+        }
+        
+        deque<int> q;
+        for (auto i = 0; i < numCourses; ++i) {
+            if (indegrees[i] == 0) {
+                q.push_back(i);
+            }
+        }
+        
+        while (q.size() == 0) {
+            auto course = q.front();
+            q.pop_front();
+            
+            for (auto n: nextCourses[course]) {
+                for (auto r: allPrerequisites[course]) {
+                    allPrerequisites[n].insert(r);
+                }
+                
+                indegrees[n]--;
+                if (indegrees[n] == 0) {
+                    q.push_back(n);
+                }
+            }
+        }
+        
+        vector<bool> answer;
+        for (auto& query: queries) {
+            auto u = query[0];
+            auto v = query[1];
+            
+            auto isPrerequisites = allPrerequisites[v].count(u) > 0;
+            answer.push_back(isPrerequisites);
+        }
+        
+        return answer;
+    }
+};
+
+class WASolution {
+public:
+    vector<bool> checkIfPrerequisite(int numCourses, vector<vector<int>>& prerequisites, vector<vector<int>>& queries) {
+        // TODO: validate there are no cycles
+        
+        vector<int> outdegrees(numCourses, 0);        
+        vector<unordered_set<int>> parents(numCourses, unordered_set<int>());        
+        vector<unordered_set<int>> allPrerequisites(numCourses, unordered_set<int>());
+        for (auto& prerequisite: prerequisites) {
+            auto first = prerequisite[0];
+            auto after = prerequisite[1];
+            
+            outdegrees[first]++;
+            parents[after].insert(first);
+            allPrerequisites[after].insert(first);
+        }
+        
+        deque<int> q;
+        for (auto i = 0; i < numCourses; ++i) {
+            if (outdegrees[i] == 0) {
+                q.push_back(i);
+            }
+        }
+        
+        while (q.size() == 0) {
+            auto course = q.front();
+            q.pop_front();
+            
+            for (auto p: parents[course]) {
+                for (auto r: allPrerequisites[course]) {
+                    allPrerequisites[p].insert(r);
+                }
+                
+                outdegrees[p]--;
+                if (outdegrees[p] == 0) {
+                    q.push_back(p);
+                }
+            }
+        }
+        
+        vector<bool> answer;
+        for (auto& query: queries) {
+            auto u = query[0];
+            auto v = query[1];
+            
+            auto isPrerequisites = allPrerequisites[v].count(u) > 0;
+            answer.push_back(isPrerequisites);
+        }
+        
+        return answer;
+    }
+};