Basic example
Input
s = "25525511135"
Output
['255.255.11.135', '255.255.111.35']
Two possible valid addresses.
Full lesson preview
Restore IP addresses from a string
Given a string of digits, produce all valid IPv4 addresses by inserting dots.
Python practice16 minRecursion & BacktrackingIntermediateLast updated March 27, 2026
Problem statement
Given a string s containing only digits, return all possible valid IPv4 addresses that can be obtained by inserting three dots into s. A valid segment is between 0 and 255 inclusive, and cannot have leading zeros unless it is exactly '0'. Return addresses in the order they are generated by a left-to-right backtracking approach. If there are no valid addresses, return an empty list.
Task
Use backtracking to place three dots to form valid IP addresses, validating each segment (0-255, no leading zeros unless the segment is '0').
Examples
Input format
A single string s. You will call restore_ip_addresses(s).
Output format
A list of strings where each string is a valid IPv4 address, e.g. ['1.1.1.1'].
Constraints
0 <= len(s) <= 20. Only digits are present in s. The final list size is limited by combinatorics of splits (max small).
Samples
Sample 1
Input
s = "0000"
Output
['0.0.0.0']
Each segment must be '0' (leading zeros not allowed otherwise).