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Decode the Coding Interview in Swift: Real-World Examples

Restore IP Addresses

Explore how to restore valid IP addresses from a string of digits by applying constrained programming and backtracking. This lesson helps you understand the problem constraints, implement an efficient algorithm, and reduce the solution space, preparing you for related coding interview questions.

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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

Swift
import Swift
func restoreIpAddresses(s: String) -> [String] {
    return []
}
Restore IP addresses exercise

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 ...