C++

1class Solution {
2public:
3    string defangIPaddr(string address) {
4        string s = "";
5        for(int i=0; address[i]; ++i)
6        {
7            if(address[i] != '.') s += address[i];
8            else 
9            {
10                s += "[.]";
11                
12            }
13        }
14        
15        return s;
16    }
17};

JavaScript

1var defangIPaddr = function(address) {
2    const regex = /\./gi;
3    return address.replace(regex, '[.]');
4};

Ruby

1def defang_i_paddr(address)
2    i = 1
3    while (i < address.length) do
4        if address[i-1] == '.'
5            address.insert(i-1, '[')
6            address.insert(i+1, ']')
7            i += 2
8        end
9        i += 1
10    end
11    address
12end