Kakuro Tool

A Tailor-Made App

User reference manual

-*-*-*- DRAFT February 12, 2020 -*-*-*-


The Kakuro Tool is intended as a trusted companion for anyone solving Kakuro puzzles on paper with pencil and eraser.

When solving Kakuros, you often need to work out exactly which digit combinations are possible for a given sum considering a number of extra constranints. While it is possible to generate these list by hand, it is a tedious, mechanical task and not one that adds to the fun of solving the puzzle.

The centre of the app is the "Kakurolator", which is a combination calculator accepting the sum and field count as primary inputs:

screenshots/Intro-0-empty.png: Not found

Consider a sum of 17 in 4 fields entered into the Kakurolator

screenshots/Intro-1-17-4.png: Not found screenshots/Intro-1-17-4-rev.png: Not found

resulting in 9 possible combinations. While solving a Kakuro there are two schools of thinking of combinations: "Bottom-up" and "Top-down" as illustrated above. Many people find it natural to see combinations "Bottom-up", i.e. starting with small digits and ending in the largest digits. However, some find it more effective to view combinations starting with the highest values because the bigger digits tend to limit the choices faster. With Kakuro Tool you can select which direction to use at any time through settings. For the remainder of this manual, we stick to the "Bottom up" direction as it seems to be the most common view especially for beginners but urge users to try out the "Reverse digit order" option as it soon becomes addictive.

Now consider this fragment of a Kakukro, which has a sum of 17 in 4 fields:

images/example-1-empty.png: Not found screenshots/Intro-1-17-4.png: Not found

To solve the 17-sum, we first consider the column with sum 30 in 4 fields. The only solution is "6 7 8 9" but the crossing rows result in some constraints, which are marked by writing the set of possible digits in each field.

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The 30-sum must have a "6" and the only possible position is as the first digit of the our 17-sum. Thus we can write the "6" and update the Kakurolator with the constraint that "6" is a "required" digit, leaving only three possible combinations.

images/example-3-add-6.png: Not found screenshots/Intro-4-require-6.png: Not found

Further checking on the remaining fields of the 17-sum reveal that none of them can contain 8: 7 is the unique sum of "1 2 4", 16 is the unique sum of "1 3", 4 is the unique sum of "1 3".

images/example-4-hori-hint.png: Not found screenshots/Intro-5-horizontal-constraints.png: Not found

We can therefore enter "8" as a "rejected" digit in the Kakurolator reducing the number of combinations to only two.

images/example-4-hori-hint.png: Not found screenshots/Intro-6-reject-8.png: Not found

To narrow down further, we look at the the available digits for the remaining three fields in the two combinations: "1 2 3 4 5 7". We cannot reject "2" and "4" because the are both possible in the second field of the 17-sum but only in that field. If we look at the two possible combinations separately, we see that we must either have both "2" and "4" (in "2 4 5 6") or none of them (in "1 3 6 7"). As we only have one field accepting "2" or "4", we can rule out using the combination "2 4 5 6". To remember the result of this analysis we can strike out the impossible combination:

images/example-4-hori-hint.png: Not found screenshots/Intro-7-strike-24.png: Not found

We are now left with only one possible digit combination for this particular sum and only need to see how these digits can fit with the crossing sums. This is the result

images/example-5-solved.png: Not found screenshots/Intro-7-strike-24.png: Not found

Kakuro puzzles are sometimes referred to as a cross-sum puzzle, stressing the main source of constraints to the digit combinations comes from the crossing of several sums. Consequently, it is very useful to be able to see several sets of possible combinations at the same time. For that reason it has been important to make each combination calculator as small as possible to fit more information into a single screen of the device and further place the Kakurolator in a scrolling screen. The maximum allowed configuration is 12 by 12 allowing for 144 simultaneous sets of combinations.

Main screen

The Kakuro Tool is focused on a single main screen, which is a 2D scrollable area containing many Kakuro caclulators, the so called "Kakurolators", organized in a number of columns holding rows of Kakurolators, which all operate independently of each other.

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All the marked elements of the main screen are described below:

Context menus

Context menus are available by long-pressing in the main screen (where all the Kakurolators are). There are two different menus; one pertaining to a specific Kakurolator; one pertaining to an entire column.

Kakurolator context menu

A long press on any of the Kakurolators will open the context menu named "Combination Menu" as shown below.

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The menu offers a choice between 4 actions. The first three pertain to the specific Kakurolator that was pressed while the final option affects the entire column. The options are:

Column context menu

A long press in an empty part of a Kakurolator column will open the context menu named "Column Menu" as shown below.

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This menu offers two choices, as follows:

Options menu

The three vertical dots to the right in the title bar opens the "options menu", which comes in one of two versions depending on whether the countdown timer is active or not:

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The available options are:


The main settings screen is opened from the "Settings" entry in the Options menu see Options menu above. The main settings screen provides access to all settings and provides some general information about the app developer and publisher as well as the specific app version, which is important, if an error needs to be reported.

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The available settings are:

Layout settings
The layout and appearance of the main screen can be controlled through these settings.

screenshots/Settings-layout.png: Not found screenshots/Settings-layout-rows.png: Not found screenshots/Settings-layout-columns.png: Not found

Three things can be changed. However, the control over Rows and Columns is not available in the Demo version. The available settings are:

Countdown timer settings

The countdown timer can be customized through these settings.

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When the countdown expires, the following dialog is presented:

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The Time expired dialog offers three choices: