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Decode the Coding Interview in Elixir: Real-World Examples

Restore IP Addresses

Explore how to restore all possible valid IP addresses from a string of digits by applying techniques like constrained programming and backtracking. Understand how to efficiently place dots and validate segments to generate IP addresses and optimize your algorithm with constant time and space complexity.

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Description

Given a string s containing only digits, you have to return all the possible IP addresses that can be obtained from the string s in a list.

The order in which IP addresses are placed in the list is not important.

A valid IP address consists of four integers, where each integer lies within the range of 0 and 255. These integers are separated by single dots . and cannot have leading zeros.

Constraints

  • The input string s consists of digits only.
  • 4 <= s.length <= 12

Let’s review a few examples below:

Coding exercise

Elixir
defmodule Solution do
  def restore_ip_addresses(_s) do    
    # Write your code here
  end
end

Solution

The naive brute force solution would be to check all possible positions of the dots and only keep the valid ones. We have 11 possible positions where we can place the dots. For the first dot ., we will have 11 possible positions, 10 for the second dot, and 9 for the third. Hence, in the worst case, we will have to perform 11×10×9=99011 \times 10 \times 9 = 990 ...