Sums (Mind Loft)

Sums is the kakuro on Mind Loft, a free site of daily browser games. Kakuro is often called a crossword of sums. The grid looks like a small crossword, and every run of white squares has a total printed in the black square at its head: the across total at top right, the down total at bottom left. Each run must be filled with digits 1 to 9 that add up to its total, with no digit repeated in the run.

The way in is the totals that can only be made one way. Three in two squares is always 1 and 2, sixteen in two is always 7 and 9, and twenty-four in three is always 7, 8 and 9. Those runs are footholds, and where one crosses another the shared square usually settles both. When you select a square, a line under the board lists every set of digits that still fits it.

Each grid has a single solution reachable by deduction. Wrong entries are not flagged, and since nothing is counted against you, the leaderboard is a straight race on the clock.

A new grid goes up at midnight US Eastern Time. Weekday boards are 7x7 (30 white squares on the day we looked) and get harder through the week; the Sunday Edition is 11x11. Mind Loft suggests Cages (killer sudoku), Sando (sandwich sudoku) and Crunch (a numbers round) for more arithmetic.