text: Find triplet such that number of nodes connecting these triplets is maximum | Python3 implementation of the approach ; To store the required nodes ; Parent array to retrace the nodes ; Visited array to prevent DFS in direction on Diameter path ; DFS function to find the startnode ; DFS function to find the endnode of diameter and maintain the parent array ; DFS function to find the end node of the Longest Branch to Diameter ; Function to find the required nodes ; To find start node of diameter ; To find end node of diameter ; x is the end node of diameter ; Mark all the nodes on diameter using back tracking ; Find the end node of longest branch to diameter ; Driver code
code: MAX = 100005 NEW_LINE adjacent = [ [ ] for i in range ( MAX ) ] NEW_LINE visited = [ False ] * MAX NEW_LINE startnode = endnode = thirdnode = None NEW_LINE maxi , N = - 1 , None NEW_LINE parent = [ None ] * MAX NEW_LINE vis = [ False ] * MAX NEW_LINE def dfs ( u , count ) : NEW_LINE INDENT visited [ u ] = True NEW_LINE temp = 0 NEW_LINE global startnode , maxi NEW_LINE for i in range ( 0 , len ( adjacent [ u ] ) ) : NEW_LINE INDENT if not visited [ adjacent [ u ] [ i ] ] : NEW_LINE INDENT temp += 1 NEW_LINE dfs ( adjacent [ u ] [ i ] , count + 1 ) NEW_LINE DEDENT DEDENT if temp == 0 : NEW_LINE INDENT if maxi < count : NEW_LINE INDENT maxi = count NEW_LINE startnode = u NEW_LINE DEDENT DEDENT DEDENT def dfs1 ( u , count ) : NEW_LINE INDENT visited [ u ] = True NEW_LINE temp = 0 NEW_LINE global endnode , maxi NEW_LINE for i in range ( 0 , len ( adjacent [ u ] ) ) : NEW_LINE INDENT if not visited [ adjacent [ u ] [ i ] ] : NEW_LINE INDENT temp += 1 NEW_LINE parent [ adjacent [ u ] [ i ] ] = u NEW_LINE dfs1 ( adjacent [ u ] [ i ] , count + 1 ) NEW_LINE DEDENT DEDENT if temp == 0 : NEW_LINE INDENT if maxi < count : NEW_LINE INDENT maxi = count NEW_LINE endnode = u NEW_LINE DEDENT DEDENT DEDENT def dfs2 ( u , count ) : NEW_LINE INDENT visited [ u ] = True NEW_LINE temp = 0 NEW_LINE global thirdnode , maxi NEW_LINE for i in range ( 0 , len ( adjacent [ u ] ) ) : NEW_LINE INDENT if ( not visited [ adjacent [ u ] [ i ] ] and not vis [ adjacent [ u ] [ i ] ] ) : NEW_LINE INDENT temp += 1 NEW_LINE dfs2 ( adjacent [ u ] [ i ] , count + 1 ) NEW_LINE DEDENT DEDENT if temp == 0 : NEW_LINE INDENT if maxi < count : NEW_LINE INDENT maxi = count NEW_LINE thirdnode = u NEW_LINE DEDENT DEDENT DEDENT def findNodes ( ) : NEW_LINE INDENT dfs ( 1 , 0 ) NEW_LINE global maxi NEW_LINE for i in range ( 0 , N + 1 ) : NEW_LINE INDENT visited [ i ] = False NEW_LINE DEDENT maxi = - 1 NEW_LINE dfs1 ( startnode , 0 ) NEW_LINE for i in range ( 0 , N + 1 ) : NEW_LINE INDENT visited [ i ] = False NEW_LINE DEDENT x = endnode NEW_LINE vis [ startnode ] = True NEW_LINE while x != startnode : NEW_LINE INDENT vis [ x ] = True NEW_LINE x = parent [ x ] NEW_LINE DEDENT maxi = - 1 NEW_LINE for i in range ( 1 , N + 1 ) : NEW_LINE INDENT if vis [ i ] : NEW_LINE INDENT dfs2 ( i , 0 ) NEW_LINE DEDENT DEDENT DEDENT if __name__ == " _ _ main _ _ " : NEW_LINE INDENT N = 4 NEW_LINE adjacent [ 1 ] . append ( 2 ) NEW_LINE adjacent [ 2 ] . append ( 1 ) NEW_LINE adjacent [ 1 ] . append ( 3 ) NEW_LINE adjacent [ 3 ] . append ( 1 ) NEW_LINE adjacent [ 1 ] . append ( 4 ) NEW_LINE adjacent [ 4 ] . append ( 1 ) NEW_LINE findNodes ( ) NEW_LINE print ( " ( { } , ▁ { } , ▁ { } ) " . format ( startnode , endnode , thirdnode ) ) NEW_LINE DEDENT