Parameter Resolver - Resolve Nested Parameter References with Dependency Ordering

Question

## Round 1 - Coding

## Problem

You have a set of named parameters. Each parameter's value is either a literal string or a template string referencing other parameters using `${name}` syntax. Implement a `ParameterResolver` that resolves all parameters to their final string values. Raise an error for circular references.

```python
class ParameterResolver:
    def __init__(self, params: dict[str, str]):
        # params: {name -> raw value, possibly containing ${other_name}}
        pass

def resolve(self, name: str) -> str:
        # Returns fully resolved string value for name
        pass

def resolve_all(self) -> dict[str, str]:
        # Returns resolved values for every parameter
        pass
```

## Example

```
params = {
  "host": "localhost",
  "port": "8080",
  "base_url": "http://${host}:${port}",
  "api_url": "${base_url}/api/v1"
}

resolver = ParameterResolver(params)
resolver.resolve("api_url")
# -> "http://localhost:8080/api/v1"
```

## Circular Error Case

```
params = {"a": "${b}", "b": "${a}"}
resolver.resolve("a")  # -> raises CircularReferenceError
```

## Follow-ups

1. How do you detect cycles efficiently? Describe the DFS-based approach with state coloring.
2. What if a parameter references a name that does not exist? Should it fail or leave the placeholder?
3. How would you support default values in the syntax, e.g. `${host:-127.0.0.1}`?
4. How would you extend this to support environment variable overrides at resolution time?

Parameter Resolver - Resolve Nested Parameter References with Dependency Ordering

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