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Curious Cheetah

Doppelblock

Background

The origin of this puzzle is unknown. Janko.at first became aware of it via Croco Puzzle.

Puzzle and Goal

An unsolved puzzle consists of a square grid with some number clues along the edge.
The goal is to color two cells in each rank black, and to fill in the rest of the cells with numbers.

Rules

The solved grid must satisfy the following conditions:

Playable Online