added course schedule with graphs

Author: mihirs16

14. Questions/leetcode 207 - course schedule.py

@@ -0,0 +1,46 @@
+# course schedule | leetcode 207 | https://leetcode.com/problems/course-schedule/
+# method: depth first search
+
+class Solution:
+    def canFinish(self, numCourses: int, prerequisites) -> bool:
+        
+        # init prequisite map
+        preqMap = {}
+        for i in range(numCourses):
+            preqMap[i] = []
+       
+        # add mentioned prerequisites 
+        for crs, pre in prerequisites:
+            preqMap[crs].append(pre)
+          
+        # init visit set
+        visitSet = set()
+        
+        # dfs
+        def checkPreq(crs):
+            
+            # if course is already visited 
+            if crs in visitSet:
+                return False 
+           
+            # if no prequisites left
+            if preqMap[crs] == []:
+                return True
+           
+            # visiting this course
+            visitSet.add(crs)
+            
+            # checking each prerequisite
+            for pre in preqMap[crs]:
+                if not checkPreq(pre): return False
+            
+            # all prerequisites are doable
+            visitSet.remove(crs)
+            preqMap[crs] = []
+            return True
+        
+        # check prerequisites for each course
+        for crs in range(numCourses):
+            if not checkPreq(crs): return False
+           
+        return True