Course Schedule Solution

Author: PDKhan

course-schedule/PDKhan.cpp

@@ -0,0 +1,80 @@
+//DFS
+class Solution {
+    public:
+        bool dfs(int curr, vector<vector<int>>& graph, vector<int>& visited){
+            if(visited[curr] == 1)
+                return false;
+            
+            if(visited[curr] == 2)
+                return true;
+    
+            visited[curr] = 1;
+    
+            for(int i = 0; i < graph[curr].size(); i++){
+                if(dfs(graph[curr][i], graph, visited) == false)
+                    return false;
+            }
+    
+            visited[curr] = 2;
+    
+            return true;
+        }
+    
+        bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
+            vector<vector<int>> graph (numCourses);
+            vector<int> visited (numCourses, 0);
+    
+            for(int i = 0; i < prerequisites.size(); i++){
+                int course = prerequisites[i][0];
+                int pre = prerequisites[i][1];
+    
+                graph[pre].push_back(course);
+            }
+    
+            for(int i = 0; i < numCourses; i++){
+                if(dfs(i, graph, visited) == false)
+                    return false;
+            }
+    
+            return true;
+        }
+    };
+
+// BFS
+class Solution {
+    public:
+        bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
+            vector<vector<int>> graph (numCourses);
+            vector<int> inDegree (numCourses, 0);
+    
+            for(int i = 0; i < prerequisites.size(); i++){
+                int course = prerequisites[i][0];
+                int pre = prerequisites[i][1];
+    
+                graph[pre].push_back(course);
+                inDegree[course]++;
+            }
+    
+            queue<int> q;
+    
+            for(int i = 0; i < numCourses; i++){
+                if(inDegree[i] == 0)
+                    q.push(i);
+            }
+    
+            int count = 0;
+    
+            while(!q.empty()){
+                int curr = q.front();
+                q.pop();
+                count++;
+    
+                for(int i = 0; i < graph[curr].size(); i++){
+                    if(--inDegree[graph[curr][i]] == 0)
+                        q.push(graph[curr][i]);
+                }
+            }
+    
+            return count == numCourses;;
+        }
+    };