"""Utilities for converting integer colorings to named colors."""
from typing import Any

COLORS = ['blue', 'red', 'green', 'yellow', 'purple']

def convert_coloring(
    coloring: dict[Any, int],
    vertices: list[Any] | None = None
) -> dict[str, list[Any]]:
    """Convert an integer coloring dict to a dict mapping color names to vertex lists."""
    colors: dict[str, list[Any]] = {}
    for k, v in coloring.items():
        if vertices and k not in vertices:
            continue
        color = COLORS[v]
        if color not in colors:
            colors[color] = []
        colors[color].append(k)
    return colors