Sumrex

Sumrex places six rex on a 6 × 6 grid divided into colored regions, and adds a constraint that placement puzzles don't usually have: a numbered target. One rex per row, one per column, one per region, never two that touch, not even diagonally, and above all, the six covered numbers must total exactly the day's target. The site sums up the promise in one line: six numbers, six rules, one sum, and guarantees a unique solution with no guessing.

1. Read the target displayed above the grid: it's the sum the six covered numbers must add up to.
2. Tap a cell once to cross it out, a second time to place a rex on it, a third time to cancel.
3. Place the six rex so there's one per row, one per column, and one per colored region, with none touching another, not even at a corner.
4. Check your total with the 'Sum' counter, then validate with 'Check'.

Because the sum changes the nature of the problem: without it, one would look for a valid placement; with it, one looks for the valid placement that hits the right total. The board displays a counter of rex placed and a sum counter, and the grid fits in six pieces.

Two counters appear above the buttons: Selected 0 / 6, which counts the rex placed, and Sum. The board also offers Clear and Reveal solution, and a help page lays out three hints without spoiling the solution.

Core play

A single default puzzle: place six rex on a 6 × 6 grid so the six covered numbers sum to the day's target. The placement rules are: one rex per row, one per column, one per colored region, and no two rex may touch, not even diagonally. The interface displays Selected (count of rex placed) and Sum counters, a Check button, Clear and Reveal solution buttons, and a help page with three progressive hints.

• A placed rex blocks its eight neighboring cells, diagonals included: in a grid this tight, each placement costs far more than its row and its column.
• The target acts as a filter, not decoration: several placements satisfy the row, column, and region rules, only one hits the correct total.
• The first tap crosses out the cell instead of placing a rex: use it like a notepad to eliminate cells whose number is incompatible with the target.