Create Find Minimum Diameter After Merging Two Trees.py

Author: erjan

Find Minimum Diameter After Merging Two Trees.py

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+'''
+There exist two undirected trees with n and m nodes, numbered from 0 to n - 1 and from 0 to m - 1, respectively. You are given two 2D integer arrays edges1 and edges2 of lengths n - 1 and m - 1, respectively, where edges1[i] = [ai, bi] indicates that there is an edge between nodes ai and bi in the first tree and edges2[i] = [ui, vi] indicates that there is an edge between nodes ui and vi in the second tree.
+
+You must connect one node from the first tree with another node from the second tree with an edge.
+
+Return the minimum possible diameter of the resulting tree.
+
+The diameter of a tree is the length of the longest path between any two nodes in the tree.
+'''
+
+class Solution:
+    def minimumDiameterAfterMerge(self, edges1: List[List[int]], edges2: List[List[int]]) -> int:
+        n = len(edges1)+1
+        m = len(edges2)+1
+
+    
+        adj1 = self.buildAdjList(n,edges1)
+        adj2 = self.buildAdjList(m,edges2)
+
+        d1 = self.find_diameter(n,adj1)
+        d2 = self.find_diameter(m,adj2)
+        comb = ceil(d1/2) + ceil(d2/2)+1
+        return max(comb, d1,d2)
+
+    def buildAdjList(self,n,e):
+
+        graph = defaultdict(list)
+        for a,b in e:
+            graph[a].append(b)
+            graph[b].append(a)
+        return graph
+
+        
+    def find_diameter(self,n,adj):
+        farthest_node,_ = self.find_farthest_node(n,adj,0)
+        _,diameter = self.find_farthest_node(n,adj,farthest_node)
+        return diameter
+
+    def find_farthest_node(self,n,adj,source_node):
+        q = deque([source_node])
+        visited = [False]*n
+        visited[source_node] = True
+        maxd = 0
+        farthest_node =source_node
+        while q:
+            for _ in range(len(q)):
+                cur = q.popleft()
+                farthest_node = cur
+                for n in adj[cur]:
+                    if not visited[n]:
+                        visited[n]=True
+                        q.append(n)
+            if q:
+                maxd+=1
+        return farthest_node,maxd