Colordoku is a logic-based, combinatorial color-placement puzzle. The objective is to fill a 9×9 grid with colors so that each column, each row, and each of the nine 3×3 sub-grids that compose the grid (also called "boxes", "blocks", "regions", or "sub-squares") contains different colors. The puzzle setter provides a partially completed grid, which for a well-posed puzzle has a unique solution.