update

Author: wuduhren

problems/python3/graph-valid-tree.py

@@ -0,0 +1,33 @@
+class Solution:
+    def validTree(self, N: int, edges: List[List[int]]) -> bool:
+        def union(n1, n2) -> bool:
+            p1 = find(n1)
+            p2 = find(n2)
+            
+            if p1==p2:
+                return False
+            elif p1<p2:
+                parents[p2] = p1
+            else:
+                parents[p1] = p2
+                
+            return True
+            
+        
+        def find(n) -> int:
+            p = parents[n]
+            while p!=parents[p]: p = find(p)
+            parents[n] = p
+            return p
+        
+        parents = [n for n in range(N)]
+
+        for n1, n2 in edges:
+            if not union(n1, n2): return False
+        
+        #check if all node trace back to the same root
+        root = find(0)
+        for n in range(1, N):
+            if root!=find(n): return False
+        
+        return True