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Defanging an IP Address

EasyUpdated: Aug 2, 2025
Practice on:
LeetCode

Problem

Given a valid (IPv4) IP address, return a defanged version of that IP address.

A defanged IP address replaces every period "." with "[.]".

Examples

Example 1

Input: address = "1.1.1.1"
Output: "1[.]1[.]1[.]1"

Example 2

Input: address = "255.100.50.0"
Output: "255[.]100[.]50[.]0"

Constraints

  • The given address is a valid IPv4 address.

Solution

Method 1 – String Replacement

Intuition

The problem is a simple string manipulation: replace every period . in the IP address with [.]. This can be done efficiently using built-in string replacement functions in most languages.

Approach

  1. Iterate through the string and replace every . with [.].
  2. Return the modified string.

Code

C++
class Solution {
public:
    string defangIPaddr(string address) {
        string ans;
        for (char c : address) {
            if (c == '.') ans += "[.]";
            else ans += c;
        }
        return ans;
    }
};
Go
func defangIPaddr(address string) string {
    ans := ""
    for _, c := range address {
        if c == '.' {
            ans += "[.]"
        } else {
            ans += string(c)
        }
    }
    return ans
}
Java
class Solution {
    public String defangIPaddr(String address) {
        return address.replace(".", "[.]");
    }
}
Kotlin
class Solution {
    fun defangIPaddr(address: String): String {
        return address.replace(".", "[.]")
    }
}
Python
class Solution:
    def defangIPaddr(self, address: str) -> str:
        return address.replace('.', '[.]')
Rust
impl Solution {
    pub fn defang_i_paddr(address: String) -> String {
        address.replace(".", "[.]")
    }
}
TypeScript
class Solution {
    defangIPaddr(address: string): string {
        return address.replace(/\./g, '[.]');
    }
}

Complexity

  • ⏰ Time complexity: O(n), where n is the length of the address, since we scan each character once.
  • 🧺 Space complexity: O(n), for the output string.

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