leetcode #210

Author: guipleite

course-schedule-ii.py

@@ -0,0 +1,52 @@
+# https://leetcode.com/problems/course-schedule-ii/submissions/
+
+class Solution(object):
+    
+    def DepthFirstSearch(self, current, visited, currentSet, ans, prereq):
+        
+            currentSet.add(current)
+            
+            if current in prereq:
+                for course in prereq[current]:
+                    
+                    if course in visited:
+                        continue
+
+                    if course in currentSet:
+                        return False
+
+                    if not self.DepthFirstSearch(course, visited, currentSet, ans, prereq):
+                        return False
+            
+            currentSet.remove(current)
+            visited.add(current)
+            
+            ans.append(current)
+            
+            return ans
+            
+    
+    def findOrder(self, numCourses: int, prerequisites: List[List[int]]) -> List[int]:
+        
+        prereq = {}
+        
+        for prerequisit in prerequisites:
+            
+            if prerequisit[0] in prereq:
+                prereq[prerequisit[0]].append(prerequisit[1])
+                
+            else:
+                prereq[prerequisit[0]] = [prerequisit[1]]
+            
+        visited = set()
+        ans = []
+        
+        for course in range(numCourses):
+
+            if course in visited:
+                continue
+            
+            if not self.DepthFirstSearch(course, visited, set(), ans, prereq):
+                return []
+            
+        return ans

path-sum-iii.py

@@ -14,21 +14,26 @@ def DepthFirstSearch(self, root, sum):
 
         if not root:
             return ans
+
+        else:
 
-        if root.val == sum:
-            ans += 1
+            if root.val == sum:
+                ans = 1
+                
+            ans += self.DepthFirstSearch(root.left,  sum - root.val)
+            ans += self.DepthFirstSearch(root.right, sum - root.val)
 
-        ans += self.DepthFirstSearch(root.left,  sum - root.val)
-        ans += self.DepthFirstSearch(root.right, sum - root.val)
-        
         return ans
 
     def pathSum(self, root: 'TreeNode', sum: 'int') -> 'int':
-        
+        ans = 0
+
         if not root:
-            return 0
+            return ans
 
         else:
-            ans = self.DepthFirstSearch(root, sum) + self.pathSum(root.left, sum) + self.pathSum(root.right, sum)
+            ans += self.DepthFirstSearch(root, sum) 
+            ans += self.pathSum(root.left,  sum) 
+            ans += self.pathSum(root.right, sum)
 
         return ans