Friedrich Ewald My Personal Website

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  • Leetcode: Merge two lists

    class Solution:
      def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
        root = ListNode()
        current = root
    
        while list1 is not None and list2 is not None:
          if list1.val < list2.val:
            current.next = ListNode(list1.val)
            current = current.next
            list1 = list1.next
          else:
            current.next = ListNode(list2.val)
            current = current.next
            list2 = list2.next
    
        if list1 is not None:
          current.next = list1
        if list2 is not None:
          current.next = list2
    
        return root.next

    Results

    Runtime: 34 ms, faster than 97.81% of Python3 online submissions for Merge Two Sorted Lists. Memory Usage: 13.9 MB, less than 79.56% of Python3 online submissions for Merge Two Sorted Lists.

  • Leetcode: All possible subsets

    A subset of a list with the elements {a,b,c} is {a,b}. The task is to find all possible subsets. Sets in programming languages are usually not ordered. Therefore, the set {a,b,c} is equivalent to {b,c,a}. The idea for the solution is a nested for-loop that iterates over the results again and again, starting with one empty ([]) result.

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  • Leetcode: Permutations

    The goal of this task is to find all possible permutations of numbers in a list. For example, [1,2,3] can become [[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1]. Mathematically, the number of possible permutations without using duplicates is n! where n is the number of unique elements in the list. This problem can best be solved by using backtracing and recursion. The general idea is to put all possible digits in the beginning and then cut off the rest of the list and repeat the first step. Later, the list is assembled. The algorithm stops if there is only one item in the list because the only possible permutation is with itself. The other special case that needs to be handled is the empty list which must return the empty list itself.

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  • How to add Devise to Rails

    Great tutorial how to use Devise with Rails 7 and Turbo: Youtube.

  • Leetcode: Letter case permutation

    The task is to print all case permutations of letters from strings that can include digits and letters. For example, a1b becomes a1b, a1B, A1b, A1B. The trick here is to realize that there are 2^n possible permutations where n is the number of characters, excluding digits.

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