♛ N-Queens Visualiser ♛

Table of Content

Content
🧩Problem Statement
🎯Objective
🖼️Preview
📖Terminology
💾About the program
🔀Flowchart
🔮Future Enhancements
🚩Development Issues
🎓Things Learnt
🔗Links

Problem Statement🧩

The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other.

Objective🎯

Given an integer n, we must display all distinct solutions to the n-queens puzzle

Preview🖼️

Main Window

Result Window

Terminology📖

• Rank
  • In chess, a rank refers to a straight full set of squares on the horizontal axis
• File
  • In chess, a file refers to a straight full set of squares on the vertical axis
• Frame
  • A frame is a window using by java
• Panel
  • A panel is a section within a frame

About the program💾

• Programming Language used

  • Java

• Package(s) used

  • java.util.Scanner
    • To take input from the user
  • java.util.List
    • To store the answer/results with a list
  • java.util.ArrayList
    • To instantiate an abstract list
  • import java.awt
    • To create Abstract Window Toolkit import javax.swing.*;
    • Easy to use GUI components

Flowchart🔀

Over View

---
title: Overview
---
flowchart
    Start([Start])
    CreateMainUI[Create the Main UI]
    RunAlgorithm[Run Algorithm]
    CreateResultUI[Create the Result UI]
    End([End])

    Start --> CreateMainUI --> RunAlgorithm --> CreateResultUI --> End

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Rendering the Live Preview

---
title: Rendering the Live Preview
---
flowchart
    StartPlaceQueen(["Start of placeQueen(Function)"])
    VisuallyPlaceQueen[Visually Place Queen]
    DecisionQueenPositionIsValid{"
        Is
        Queen placed at
        Valid Square
    "}
    VisuallyRemoveQueen["
        Visually Remove
        Last Placed Queen
    "]
    BackTrack([Perform Back Tracking])
    EndPlaceQueen(["
        Run placeQueen()
        for next queen
    "])

    
    StartPlaceQueen --> VisuallyPlaceQueen --> CheckingForOtherQueens
    
    %% Checking for other queens
    subgraph CheckingForOtherQueens [Checking for other queens]
        direction TB
        StartChecking([Start Checking])
        CheckReturnStateSameFile{"
            Is
            The file clear of
            other queens
        "}
        CheckReturnStateLeftDiagonal{"
            Is
            The Left Diagonal
            clear of other queens
        "}
        CheckReturnStateRightDiagonal{"
            Is
            The Right Diagonal
            clear of other queens
        "}
        
        ReturnTrue([Return True])
        ReturnFalse([Return False])
        
        %% SubgraphSameFileCheck
        subgraph SubgraphSameFileCheck [Checking in the same file]
            direction TB
            SameFileCheckIfSquareIsValid{"
                If
                Square
                is Valid
            "}
            SameFileHighlightValid["HighLight as Valid Square✅"]
            SameFileSqaureWithinOfBoard{"
                Is
                Next Sqaure on
                the same file still
                within the Board
            "}
            SameFileReturnTrue([Return true])
            SameFileHighlightInvalid["HighLight as Invalid Square❌"]
            SameFileNavigateToNextSquare["
                Navigate to Next Square
                of Same File
            "]
            SameFileClearHighlights[Clear All Highlights]
            SameFileRevertPosition["
                Revert board position to
                last non-conflict position
            "]
            SameFileReturnFalse([Return false])
            
            %% SameFileCheckIfSquareIsValid
                SameFileCheckIfSquareIsValid --> |Yes🟢| SameFileHighlightValid --> SameFileNavigateToNextSquare --> SameFileSqaureWithinOfBoard 
                SameFileCheckIfSquareIsValid --> |No🔴| SameFileHighlightInvalid --> SameFileClearHighlights --> SameFileRevertPosition --> SameFileReturnFalse
            
            %% SameFileSqaureWithinOfBoard
                SameFileSqaureWithinOfBoard -->|Yes🟢| SameFileCheckIfSquareIsValid
                SameFileSqaureWithinOfBoard -->|No🔴| SameFileReturnTrue
        end

        %% SubgraphLeftDiagonalCheck
        subgraph SubgraphLeftDiagonalCheck [Checking in the Left Diagonal]
            direction TB
            LeftDiagonalCheckIfSquareIsValid{"
                If
                Square
                is Valid
            "}
            LeftDiagonalHighlightValid["HighLight as Valid Square✅"]
            LeftDiagonalSqaureWithinOfBoard{"
                Is
                Next Sqaure on
                the Left Diagonal still
                within the Board
            "}
            LeftDiagonalReturnTrue([Return true])
            LeftDiagonalHighlightInvalid["HighLight as Invalid Square❌"]
            LeftDiagonalNavigateToNextSquare["
                Navigate to Next Square
                of Left Diagonal
            "]
            LeftDiagonalClearHighlights[Clear All Highlights]
            LeftDiagonalRevertPosition["
                Revert board position to
                last non-conflict position
            "]
            LeftDiagonalReturnFalse([Return false])
            
            %% LeftDiagonalCheckIfSquareIsValid
                LeftDiagonalCheckIfSquareIsValid --> |Yes🟢| LeftDiagonalHighlightValid --> LeftDiagonalNavigateToNextSquare --> LeftDiagonalSqaureWithinOfBoard 
                LeftDiagonalCheckIfSquareIsValid --> |No🔴| LeftDiagonalHighlightInvalid --> LeftDiagonalClearHighlights --> LeftDiagonalRevertPosition --> LeftDiagonalReturnFalse
            
            %% LeftDiagonalSqaureWithinOfBoard
                LeftDiagonalSqaureWithinOfBoard -->|Yes🟢| LeftDiagonalCheckIfSquareIsValid
                LeftDiagonalSqaureWithinOfBoard -->|No🔴| LeftDiagonalReturnTrue
        end

        %% SubgraphRightDiagonalCheck
        subgraph SubgraphRightDiagonalCheck [Checking in the Right Diagonal]
            direction TB
            RightDiagonalCheckIfSquareIsValid{"
                If
                Square
                is Valid
            "}
            RightDiagonalHighlightValid["HighLight as Valid Square✅"]
            RightDiagonalSqaureWithinOfBoard{"
                Is
                Next Sqaure on
                the Right Diagonal still
                within the Board
            "}
            RightDiagonalReturnTrue([Return true])
            RightDiagonalHighlightInvalid["HighLight as Invalid Square❌"]
            RightDiagonalNavigateToNextSquare["
                Navigate to Next Square
                of Right Diagonal
            "]
            RightDiagonalClearHighlights[Clear All Highlights]
            RightDiagonalRevertPosition["
                Revert board position to
                last non-conflict position
            "]
            RightDiagonalReturnFalse([Return false])
            
            %% RightDiagonalCheckIfSquareIsValid
                RightDiagonalCheckIfSquareIsValid --> |Yes🟢| RightDiagonalHighlightValid --> RightDiagonalNavigateToNextSquare --> RightDiagonalSqaureWithinOfBoard 
                RightDiagonalCheckIfSquareIsValid --> |No🔴| RightDiagonalHighlightInvalid --> RightDiagonalClearHighlights --> RightDiagonalRevertPosition --> RightDiagonalReturnFalse
            
            %% RightDiagonalSqaureWithinOfBoard
                RightDiagonalSqaureWithinOfBoard -->|Yes🟢| RightDiagonalCheckIfSquareIsValid
                RightDiagonalSqaureWithinOfBoard -->|No🔴| RightDiagonalReturnTrue
        end
        
        StartChecking --> SubgraphSameFileCheck --> CheckReturnStateSameFile
        %% CheckReturnStateSameFile
            CheckReturnStateSameFile --> |Yes🟢| SubgraphLeftDiagonalCheck
            CheckReturnStateSameFile --> |No🔴| ReturnFalse

        SubgraphLeftDiagonalCheck --> CheckReturnStateLeftDiagonal
        %% CheckReturnStateLeftDiagonal
            CheckReturnStateLeftDiagonal --> |Yes🟢| SubgraphRightDiagonalCheck
            CheckReturnStateLeftDiagonal --> |No🔴| ReturnFalse
        
        SubgraphRightDiagonalCheck --> CheckReturnStateRightDiagonal
        %% CheckReturnStateRightDiagonal
            CheckReturnStateRightDiagonal --> |Yes🟢| ReturnTrue
            CheckReturnStateRightDiagonal --> |No🔴| ReturnFalse
    end


    CheckingForOtherQueens --> DecisionQueenPositionIsValid
    

    %% DecisionQueenPositionIsValid
        DecisionQueenPositionIsValid --> |Yes🟢| EndPlaceQueen
        DecisionQueenPositionIsValid --> |No🔴| VisuallyRemoveQueen
    
    VisuallyRemoveQueen --> BackTrack

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Future Enhancements🔮

• Better error handling

  • Implement error handling when a non-valid integer is entered as the number of queens
  • Implement error handling for the function buttonCompute.addActionListener()

Development Issues Faced🚩

• Stretched out grid when using GridLayout

  • Cause of the problem

    • Grid Layout did not respect the panel's preferred size

  • Solution

    • Set the size of panel with the grid layout with setPreferredSize instead of setSize, example:
      • Use:

        panelChessBoard.setPreferredSize(new Dimension(boardLength, boardLength));

      • Instead of:

        panelChessBoard.setSize(boardLength, boardLength);

    • Add the panel to the Frame using a wrapper:

      JPanel wrapperPanel = new JPanel(new FlowLayout(FlowLayout.CENTER));
      wrapperPanel.add(panelLivePreview);
      frameMain.add(wrapperPanel);
      frameMain.pack();

Things Learnt🎓

• Using packages catered for rendering graphical items
• Handling threads

Links🔗

• About the problem:
  • By LeetCode
• Completed project reference:
  • By GSR
• Drawing a chess board in Java:
  • By GUIProjects