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Given a head of a list with pointers to next and a random element, copy the list to a new list without any random pointers pointing to the old list.
One way to solve this is to copy first all the nodes into a new list via the next links. Next, we create two pointers, one pointing at the original list and the other one pointing at the new list. We then iterate over the original list (while moving the second pointer as well) and check at each step if we hit our current node in the original list via random. If we do, we make a connection in the new list as well. One specialty is that two random pointers can point at the same element. For this reason, we cannot simply stop once we found the first pointer but have to continue until the end.
Runtime: 106 ms, faster than 5.23% of Python3 online submissions for Copy List with Random Pointer. Memory Usage: 15 MB, less than 46.50% of Python3 online submissions for Copy List with Random Pointer.
About the author
Friedrich Ewald is an experienced Software Engineer with a Master's degree in Computer Science. He started this website in late 2015, mostly as a digital business card. He is interested in Go, Python, Ruby, SQL- and NoSQL-databases, machine learning and AI and is experienced in building scalable, distributed systems and micro-services at multiple larger and smaller companies.