## Lyto Different Color AI

Lyto Different Color is a color differentiation game on Facebook. Each level, there are NxN circles on a board, with one circle having a color slightly different from all the others. The player must find the circle with different color and click on it in order to go to the next level. During the early stage of the game, the difference between the color of the unique circle and the color of the other circles gets smaller, and N gets larger, making it become more difficult. For most people, level 50 is considered a high score, and it is almost impossible for a normal human to reach level 100.

I simply wanted to break this limit, so I wrote a Python script for continuously taking a snapshot of the section of the game screen, find the circles, reading their color, and pressing on the circle with unique color. It is comparatively easy for the AI to recognize the differences, since it reads the colors as an RGB value, where any difference in the values represents a difference in color.

Python Imaging Library (PIL) is used for capturing the game screen, which approximate takes a screenshot every 0.7 seconds. Afterwards, the boundary of the circles is found by finding pixels that have a different color compared with the plain background color. Then, N is found by counting continuous blocks of identical colors from a 1D diagonal slice of array from the top-left to bottom-right corner of the boundary. By finding these values, the center of every circle can be located, which the program retrieves the colors from and compare them. At last, the circle with unique color is found, and the program sends a signal to the mouse for pressing on the target position. Fig. 1 illustrates a graphical description of the program algorithm.

Figure 1. Graphical description of the algorithm for Lyto Different Color AI.

Here’s a clip of the program playing the game (2x speed):

## Minesweeper AI

I got addicted to Minesweeper the first few days when I started playing this awesome puzzle game. Solving the game faster every few times gives me great satisfaction of self-fulfillment. However, for the “expert” board setting, where 99 mines are hidden within a 16×30 square grid, I had never obtained a score lower than 100 seconds. Curious of what the fastest solving rate is the one can achieve, I designed a Minesweeper AI program that can automatically play the Windows Minesweeper game.

C language is used for programming, and the algorithm flowchart is displayed in Fig. 1.

Figure 1. Algorithm flowchart of the Minesweeper AI program.

Here breadth-first-search (BFS) is used to search for uncovered squares on the grid, and a queue is used for saving uncovered squares to be analyzed. A game-playing optimized algorithm is written inside the program, and OpenCV is used to take a snapshot of the Minesweeper window region and process the image for subsequent calculations. Mouse movement and click actions are realized by including the windows.h header.

The usage of the program is relatively simple. The user should only execute the Minesweeper game program, and modify the game setting beforehand. After opening the AI .exe file, the program will automatically locate the Minesweeper game, calculate the dimensions, then start playing. If a mine is accidentally clicked, the program will continue to play the next game until a fully uncovered board is achieved.

Here is a clip demonstrating the Minesweeper AI playing an expert level game and winning in 7 seconds. It failed on the first try almost at the end, but succeeded on the second try.

[Download program for the Minesweeper AI (Can only run on a windows 64-bit OS)]

## Guess the Number AI

After completing the first two projects of the Guess the Number series (Guess the Number (Windows) and Guess the Number (iOS)), I made an AI that can play this game at a high-human level.

It has been proven that at most 7 turns are needed to guess the answer, with a best average game length of 5.21 turns. For this game, all the possible combinations (e.g. “0123”, “7381” …) can be saved into a 1D array. After each guess, the possible combinations for the answer will be reduced. Therefore, the algorithm of the program is written for finding a number that will minimize the maximum possible combinations left. The time complexity for each turn is O(n3), and an average of 5 turns of guessing if needed for an arbitrarily chosen number.

For using the program, the user must first choose a 4-digit answer (e.g. “0123”), and input the two numbers [A] and [B] according to the game rules and the numbers guessed by the program. For instance, if the answer is “1357”, and the AI guesses “3127”, the user must input 1 2 ([A] = 1, [B] = 2).

Here’s a demonstration of the AI program guessing the answer “8192” in 5 guesses:

## Nonogram AI

Nonograms (also known as Picross, Griddlers, Pic-a-Pix, and various other names) are picture logic puzzles, in which the cells in the grid must be colored or left blank according to the numbers on the side of the grid to display hidden pictures.

Figure 1. The initial and complete state of a 25×25 grid Nonogram.
(Source: https://www.nonograms.org/nonograms/i/32344 )

For a classical type of game, the numbers are a form of discrete tomography that measures how many unbroken lines of filled-in squares there are in any given row or column. For example, a clue of “1 2 3” would mean there are sets of one, two, and three filled squares, in that order, with at least one blank square between successive sets.

Solving Nonograms can be very time-consuming, and can be tremendously brain-twisting as the grid size increases, thus I created an AI program for automatically solving these puzzles.

The program utilizes the depth-first search algorithm that runs recursively from the top to bottom row. For the jth column of the ith row, the black or blank spaces must satisfy the tomographic rules formed by the numbers of the current row and column. This is a relatively simple approach for calculating the answer. However, because the algorithm does not solve the game using a more intuitive method for solving interrelated constraints, it will use a lot of time for big grids (over 40×40).

For the input format of this program, two numbers indicating the number of rows and columns are given first (n and m). Afterwards, there are n rows of data, with each row k starting with a number nk indicating how many numbers are given in that row, and followed by nk numbers representing the discrete tomography of black spaces of that very row; then there are m rows of data, and also starting with a number mk for the kth row, and followed by mk numbers representing the discrete tomography of black spaces for the kth column.

Here’s an example input for the Nonogram in Fig. 1:

25 25
1 8
2 7 3
1 16
2 11 4
2 13 2
2 14 2
1 18
2 8 4
2 6 4
2 5 5
3 4 2 2
3 4 3 1
3 3 2 1
2 3 2
2 3 2
3 2 1 4
3 2 1 4
3 2 1 4
3 3 1 4
2 5 4
1 11
1 10
1 5
1 5
1 6
1 1
1 2
1 2
1 4
1 11
1 13
1 15
2 9 3
2 8 3
3 7 5 2
3 7 3 4
3 6 2 3
3 8 3 2
2 13 2
2 10 2
3 5 5 3
4 4 1 4 6
4 1 2 2 8
3 3 1 10
4 3 1 4 4
4 2 1 2 3
3 2 1 2
2 2 1
2 2 1
1 1

A demonstration for using the AI program for solving a 39×50 Nonogram in about 22 seconds is shown below. The result displays an owl sitting on a branch (Fig. 2).

Figure 2. The complete state of a 39×50 Nonogram displaying an owl on a branch.

## Othello AI

Othello (a variant of the traditional game Reversi) is a two-player strategy board game played on an 8×8 square field, where each player takes turns placing black or white pieces and capturing the other player’s pieces.

Figure 1. Othello board game.

The Othello AI program is the second board game AI that I have written in junior high school (the first is the Tic-Tac-Toe AI). Just like the programming strategy for the tic-tac-toe AI, I used the logic thinking experiences that I had learned while playing this game, and hard-coded some summarized strategies into this program.

Compared with the tic-tac-toe AI, which has a game-tree complexity of 9! = 362880, Othello is much more complex, yielding a stunning complexity of approximately 1058. This makes the game still mathematically unsolved up to this very day. Therefore, instead of calculating the definite winning strategy, this Othello AI rather tries to find relative advantageous points (e.g. the corners), and moves that will temporarily maximize the number of pieces which it occupies by the coded algorithm, making it a beginner ~ intermediate level AI.

Here is a demonstration of using the Othello AI program:

[Source code for the Othello AI program (Visual Basic 6.0 form file)]

## Sudoku AI

Sudoku is a commonly known logic puzzle game, and had been one of my favorite puzzle games.

Having the experience for creating the simple Tic-Tac-Toe AI, I started to take on this challenge for creating an AI that can solve Sudoku.

Figure 1. The initial and complete board state of an expert-level Sudoku game.

I had written this AI program when I was in junior high school using Visual Basic 6.0. Having no prior knowledge for algorithms and data structures (which I learned in senior high school), I came up with a rough version of the backtracking algorithm myself, and implemented it on the AI. Here, the backtracking algorithm is a kind of depth-first search (DFS), and is guaranteed for finding a valid solution. Constraint programming is also integrated with the backtracking algorithm, since it is a very intuitive way for solving the puzzle.

Here is a clip demonstrating the Sudoku Solver program solving a hard-level Sudoku in around 5 seconds:

Here is another one that solved an expert-level Sudoku in around 44 seconds:

[Source code for the Sudoku Solver (Visual Basic 6.0 form file)]

## Gomoku AI

Although entering a department different from Computer Science (CS), I still had a majority of acquainted people in NTU-CS. One day, a friend of mine who was studying in CS challenged me of making an AI of some board game. The two of us would make AIs of that game and try to win the other one using the AI. Thinking it might be some challenging but interesting subject, I started to make this Gomoku AI.

Figure 1. Game playing demonstration of the Gomoku AI program.

Being a board game with so many possible states (more than the Othello AI I had made when I was in junior high school, which only has a 8×8 grid) , it is considered overly time wasting for the AI to traverse all the possible combinations, even just within 10 moves! Game tree graphs, graph traversal algorithms (e.g. DFS, BFS) and optimal searching algorithms (e.g. Alpha–beta pruning, A*) are usually implemented for decreasing computational time and achieving the best strategy. In this project, I only used the depth-first search (DFS) algorithm, along with some hard coded optimization decisions to create this program. Although being able to place a few initial pieces successfully, the program suffers from a large amount of computational time being spent. Most of the time after a few moves, the program will just run for a few hours (or days) before taking the next move, which is obviously very a serious problem for the AI.

Nevertheless, the environment and rules of the Gomoku game engine was successfully constructed, which allowed two players to play against each other. Nowadays, these board game AI are usually designed using deep neural networks, such as AlphaGomoku, an Alpha-Go-based Gomoku AI. Constructing these AIs would be a possible future work for optimizing this game agent.

## Tic-Tac-Toe AI

Artificial intelligence (AI) has long inspired me, and had spurred me on to come up with interesting programs or projects that I had not imagined before. Since great oaks from little acorns grow, this tic-tac-toe AI project is the first and one of the most important programs I have made that can be said to possess artificial intelligence. (~age 15, 2011)

Either with the player playing first or the computer, the AI will never lose! Being a very simple game that one could easily master, tic-tac-toe can yet be quite complex in a way in that there is actually a total of 255168 possible outcomes! Fig. 1 illustrates all the possible board states until the 5th move using an optimal strategy with the 1st move at the center (States that can arise from mirroring or rotating the shown states are excluded). The green circled states are those which the circles have won, and the yellow ones are those which the circles will eventually win while continuing to implement the optimal strategy. We can see that it actually gets quite complicated after the 3rd move.

Figure 1. Possible states of Tic-Tac-Toe until the 5th move starting from the center.

Since back then I knew nothing about algorithms (which I had started to learn at senior high school), I hard coded almost all the conditions using very basic syntax: If…Else…End If and For…Loop. The AI will sometimes move randomly, but it will always follow an optimized strategy. It took me ~650 lines of code and several days of hard work to complete.

This project demonstrated the possibility of programs to achieve human level performance for playing simple games. Although objectively not considered an astonishing one, I was surely amazed and unprecedentedly inspired by the potential of programming algorithms for AI; which further on motivated me to create AI programs of increasing difficulties (refer to Gomoku AI, Sudoku AI, Othello AI, Nonogram AI, Guess the Number AI, Minesweeper AI).