Wednesday, March 16, 2011

Linked List Question

Q: Given a linked list with two pointers in node structure where one points to the next node and the other pointer points to some random node in the linked list. Write a program to create a copy of this linked list

The above problem can be solved in O( n ) time and in constant space complexity. Assuming the Node Structure as following..


1)[Merge listst]Create list B this way: for each NodeA in A create a NodeB in B , copy NEXT ptr to NodeB: NodeB{NEXT} = NodeA{NEXT} and change NEXT ptr in NodeA to this newly created node in B: NodeA{NEXT}=NodeB;
2) go through the list A (NB: you have to jump through the nodes of B!) and set NEXTRND ptr in next B nodes to the next ptrs after next_random nodes: NodeA{NEXT}{NEXTRND}=NodeA{NEXTRNF}{NEXT};
After that all NEXTRND nodes in list B will be pointing to correct nodes in B;
3) [Un-merge]. For each node in A and in NEXT node B set correct NEXT ptrs:
while(node){tmp = node{NEXT}; node{NEXT}=tmp?tmp{NEXT}:NULL; node=tmp;}
After this process all {NEXT} nodes in both lists A and B will be correct

Java Code:

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