Remove duplicates from a linked list in single traversal

Given an unsorted linked list, write a function which deletes any duplicate nodes from the list by traversing the list only once.


For example,

Input:  5 -> 3 -> 4 -> 2 -> 5 -> 4 -> 1 -> 3 -> null
Output: 5 -> 3 -> 4 -> 2 -> 1 -> null



Simple solution would be to consider every distinct pair of nodes in the list and check if they have same data or not. If their data matches we delete the latter node. The time complexity of this solution is O(n2).

We can perform better by using hashing. The idea is to traverse the given list and insert each encountered node into a set. Now, if the current node already present in the set (i.e. it is seen before), we delete it and move to next element. At the end, we will have all duplicated removed from the list.


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5 -> 3 -> 4 -> 2 -> 1 -> null


The time complexity of above solution is O(n) and auxiliary space used by the program is O(n).

Read: Remove duplicates from a sorted linked list

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I’m not going to take the bait, but I feel like the above algorithm can be written in five lines of python, which has built in hashed sets.