Implement templated string replacement

You are given:

1. A dictionary (map) of placeholder keys to values, for example:

values = {
  "db_host": "example.com",
  "db_port": 5001
}

2. A template string that may contain placeholders wrapped in double curly braces {{ and }}, for example:

"application is now connecting to {{db_host}}:{{db_port}}"

Task 1

Implement a function that replaces each placeholder in the template string with the corresponding value from the dictionary. For the example above, the output should be:

"application is now connecting to example.com:5001"

Assume:

• All placeholders appearing in the template exist as keys in the dictionary.
• Placeholders consist of letters, digits, and underscores only.

Describe your approach and then implement the function in a programming language of your choice.

Task 2 (Follow-up)

Now, instead of a single template string, you are given another dictionary where each value is a template string that may contain the same kind of {{key}} placeholders, and you are also given the same values dictionary used for substitution.

Example:

values = {
  "db_host": "example.com",
  "db_port": 5001
}

templates = {
  "conn_msg": "application is now connecting to {{db_host}}:{{db_port}}",
  "short_msg": "{{db_host}}:{{db_port}}"
}

Implement a function that takes values and templates and returns a new dictionary where each value in templates has had its placeholders replaced using values.

Explain your algorithm, including its time complexity in terms of:

• L = total length of all template strings
• K = number of distinct keys in the values dictionary.

Part 1: Replace Placeholders in a Single Template String

You are given a dictionary values that maps placeholder keys to values, and a template string that may contain placeholders in the form {{key}}. Replace every placeholder with its corresponding value from the dictionary and return the fully rendered string.

All placeholders are well-formed, every placeholder key exists in values, and keys contain only letters, digits, and underscores. If a value in values is not already a string, convert it to text before inserting it.

Constraints

• 0 <= len(template) <= 100000
• 0 <= len(values) <= 100000
• Every placeholder in template is well-formed as {{key}}
• Every placeholder key appearing in template exists in values
• Keys contain only letters, digits, and underscores

Examples

Example 1

Input: ({"db_host": "example.com", "db_port": 5001}, "application is now connecting to {{db_host}}:{{db_port}}")
Output: "application is now connecting to example.com:5001"

Explanation: Both placeholders are replaced with their mapped values.

Example 2

Input: ({}, "plain text only")
Output: "plain text only"

Explanation: Edge case: the template contains no placeholders, so it is returned unchanged.

Hints

1. Scan the template from left to right. When you see {{, keep moving until you find the matching }} to extract the key.
2. Build the answer using a list of string pieces and join at the end, instead of repeatedly concatenating strings.

Part 2: Replace Placeholders Across a Dictionary of Template Strings

You are given two dictionaries:

• values: maps placeholder keys to values
• templates: maps names to template strings

Each template string may contain placeholders in the form {{key}}. Return a new dictionary with the same keys as templates, where every template string has been rendered using values.

All placeholders are well-formed, every placeholder key exists in values, and keys contain only letters, digits, and underscores. Non-string replacement values should be converted to text before insertion.

Constraints

• 0 <= len(templates) <= 100000
• Let L be the total length of all strings in templates; L can be up to 200000
• Let K be the number of distinct keys in values
• Every placeholder in every template is well-formed as {{key}}
• Every placeholder key appearing in any template exists in values
• Keys contain only letters, digits, and underscores

Examples

Example 1

Input: ({"db_host": "example.com", "db_port": 5001}, {"conn_msg": "application is now connecting to {{db_host}}:{{db_port}}", "short_msg": "{{db_host}}:{{db_port}}"})
Output: {"conn_msg": "application is now connecting to example.com:5001", "short_msg": "example.com:5001"}

Explanation: Both template strings are rendered using the same values dictionary.

Example 2

Input: ({"db_host": "example.com"}, {})
Output: {}

Explanation: Edge case: if there are no templates, the result is an empty dictionary.

Hints

1. Solve one template string at a time using the same parsing idea as in the single-template version.
2. If some values are integers, convert each values[key] to a string once before processing all templates.