Create course-schedule-iv.py

Author: kamyu104

Python/course-schedule-iv.py

@@ -0,0 +1,52 @@
+# Time:  O(n^3)
+# Space: O(n^2)
+
+class Solution(object):
+    def checkIfPrerequisite(self, n, prerequisites, queries):
+        """
+        :type n: int
+        :type prerequisites: List[List[int]]
+        :type queries: List[List[int]]
+        :rtype: List[bool]
+        """
+        def floydWarshall(n, graph): 
+            reachable = set(map(lambda x: x[0]*n+x[1], graph)) 
+            for k in xrange(n): 
+                for i in xrange(n): 
+                    for j in xrange(n): 
+                        if i*n+j not in reachable and (i*n+k in reachable and k*n+j in reachable):
+                            reachable.add(i*n+j)
+            return reachable
+
+        reachable = floydWarshall(n, prerequisites)
+        return [i*n+j in reachable for i, j in queries]
+
+
+# Time:  O(n * q)
+# Space: O(p + n)
+import collections
+
+
+class Solution2(object):
+    def checkIfPrerequisite(self, n, prerequisites, queries):
+        """
+        :type n: int
+        :type prerequisites: List[List[int]]
+        :type queries: List[List[int]]
+        :rtyp
+        """
+        graph = collections.defaultdict(list)
+        for u, v in prerequisites:
+            graph[u].append(v)
+        result = []
+        for i, j in queries:
+            stk, lookup = [i], set([i])
+            while stk:
+                node = stk.pop()
+                for nei in graph[node]:
+                    if nei in lookup:
+                        continue
+                    stk.append(nei)
+                    lookup.add(nei)
+            result.append(j in lookup)
+        return result