LeetCode in Kotlin

93. Restore IP Addresses

Medium

A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros.

• For example, "0.1.2.201" and "192.168.1.1" are valid IP addresses, but "0.011.255.245", "192.168.1.312" and "192.168@1.1" are invalid IP addresses.

Given a string s containing only digits, return all possible valid IP addresses that can be formed by inserting dots into s. You are not allowed to reorder or remove any digits in s. You may return the valid IP addresses in any order.

Example 1:

Input: s = “25525511135”

Output: [“255.255.11.135”,”255.255.111.35”]

Example 2:

Input: s = “0000”

Output: [“0.0.0.0”]

Example 3:

Input: s = “101023”

Output: [“1.0.10.23”,”1.0.102.3”,”10.1.0.23”,”10.10.2.3”,”101.0.2.3”]

Constraints:

• 1 <= s.length <= 20
• s consists of digits only.

Solution

class Solution {
    fun restoreIpAddresses(s: String): List<String> {
        val results: MutableList<String> = ArrayList()
        step(s, 0, IntArray(4), 0, results)
        return results
    }

    fun step(s: String, pos: Int, octets: IntArray, count: Int, results: MutableList<String>) {
        if (count == 4 && pos == s.length) {
            results.add(
                octets[0].toString() + '.' +
                    octets[1] +
                    '.' +
                    octets[2] +
                    '.' +
                    octets[3],
            )
        } else if (count < 4 && pos < 12) {
            var octet = 0
            for (i in 0..2) {
                if (pos + i < s.length) {
                    val digit = s[pos + i] - '0'
                    octet = octet * 10 + digit
                    if (octet < 256) {
                        octets[count] = octet
                        step(s, pos + i + 1, octets, count + 1, results)
                    }
                    if (i == 0 && digit == 0) {
                        break
                    }
                }
            }
        }
    }
}

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