updates

Author: wuduhren

problems/python3/number-of-connected-components-in-an-undirected-graph.py

@@ -0,0 +1,25 @@
+class Solution:
+    def countComponents(self, N: int, edges: List[List[int]]) -> int:
+        def union(n1, n2):
+            p1 = find(n1)
+            p2 = find(n2)
+            if p1==p2:
+                return
+            elif p1<p2:
+                parents[p2] = p1
+            else:
+                parents[p1] = p2
+            
+        def find(n):
+            p = parents[n]
+            while p!=parents[p]: p = find(p)
+            parents[n] = p
+            return p
+        
+        parents = {n:n for n in range(N)}
+        for n1, n2 in edges: union(n1, n2)
+        
+        groups = set()
+        for n in range(N): groups.add(find(n))
+            
+        return len(groups)

problems/python3/redundant-connection.py

@@ -0,0 +1,32 @@
+class Solution:
+    def findRedundantConnection(self, edges: List[List[int]]) -> List[int]:
+        def union(n1, n2):
+            p1 = find(n1)
+            p2 = find(n2)
+            
+            if p1==p2:
+                return False #union failed, already united.
+            elif p1<p2:
+                roots[p2] = p1
+            else:
+                roots[p1] = p2
+        
+            return True #union success
+        
+        def find(n):
+            if n not in roots:
+                roots[n] = n
+                return n
+            
+            p = roots[n]
+            while p!=roots[p]:
+                p = find(p)
+            roots[n] = p
+            return p
+        
+        roots = {}
+        
+        for n1, n2 in edges:
+            if not union(n1, n2): return (n1, n2)
+        
+        return 'ERROR'