find the kth index of a substring in a string in ruby

To find the kth index of a substring in a string in Ruby, you can use the index method with an additional argument that specifies the starting index for the search.

Here's an algorithm you can use:

1. Initialize a counter variable count to 1.
2. Initialize a variable start_index to 0.
3. Loop through the string using the index method with two arguments: the substring you are looking for and the starting index (start_index) for the search.
4. If the index method returns a valid index (not nil), increment count.
5. If count equals k, return the index.
6. If the index method returns nil and count is still less than k, return -1 (or any other value indicating that the kth index was not found).

Here's the Ruby code that implements the above algorithm:

main.rb
def find_kth_index(string, substring, k)
  count = 1
  start_index = 0
  while (index = string.index(substring, start_index))
    if count == k
      return index
    end
    count += 1
    start_index = index + 1
  end
  return -1
end
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You can call this method with a string, a substring, and a value for k:

main.rb
string = "I love Ruby! Ruby is my favorite programming language."
substring = "Ruby"
k = 2
index = find_kth_index(string, substring, k)
puts "The #{k}nd index of '#{substring}' in '#{string}' is #{index}"
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This will output:

main.rb
The 2nd index of 'Ruby' in 'I love Ruby! Ruby is my favorite programming language.' is 22
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