Here is a brief description of the program and how it works.

if this if first run,
    setupBoard()
else
    get the values of the cells from what was submitted
    calculatePossibles()
    attemptToSolve()
    checkBoard()
        if no solution solution possible give message "Unable to solve as this Sudoku has no solution"
        if solved give message "Successfully Solved!"
        if we haven't been able to solve give message "Unable to solve using smart logic."
    displayBoard()
exit program

function attemptToSolve()
{
    displayBoard()
    if not yet solved, test1()
    if not yet solved, test2r()
    if not yet solved, test2c()
    if not yet solved, test2s()
    if not yet solved, test3r()
    if not yet solved, test3c()
    if not yet solved, test4r()
    if not yet solved, test4c()
}

function checkBoard()
{
    if all cells are filled, return "finished"
    loop through all cells
        if cell is empty and possible is empty return "UNABLE TO PROCEED: Found that unsolved cell has no POSSIBLES"
    return "not finished, and we can continue working"
}

function setupBoard()
{
    if the size of the board is not valid (ie. it is not a square of a smaller number)
        echo "<p>The number of digits must be a square of a smaller number. Valid selections are 4 (the square of 2), 9 (the square of 3), 16 (the square of 4), etcetera.</p>";
    else
        setup the grid
        Draw the grid and allow the user to enter some numbers
        displayBoard()
}

function displayBoard()
{
    loop through all the rows
        loop through all the columns
            draw a square and put in the value of that cell
}

function countArray($arrayToCount)
{
    loop through all the rows
        loop through all the columns
            if cell is not empty, count it
    return count;
}

function calculatePossibles()
{
    Initially a cell can be any number, we build a string of all the possible values that looks like this "123456789" for a 9x9 puzzle, or "123456789abcdefg" for a 16x16 puzzle
    create an array called 'possibles' and put the string in each cell
    Now we start looking through the grid and if there is a number filled in, we remove it from the possibles
    loop through all the rows
        loop through all the columns
            if cells has a value
                possibles for this cell is emptied
                removePossible()
}

function removePossible()
{
    remove this number from the rest of the possibles in this COLUMN
    remove this number from the rest of the possibles in this ROW
    remove this number from the rest of the possibles in this SQUARE
    first we figure out which square we are in.
}

function setCell()
{
    check for a match in this column
    check for a match in this row
    check for a match in this square
    if no matches were found
        set cell value
        removePossible()
}

function test1()
{
    // Finds cells that have only a single possible answer. If that's the only possible number for that cell, then it must be the number for that cell.
    loop through all the rows
        loop through all the columns
            if possibles is only 1 digit
                setCell()
                recursively attemptToSolve()
}

function test2r()
{
    // finds where a number is only possible once in a ROW
    // if that's the only place in the column it COULD go, then that's where it MUST go
    loop through all the rows
        loop through all the numbers (1 to 9)
            if there's only one place it can be
                setCell()
                recursively attemptToSolve()
}

function test2c()
{
    // finds where a number is only possible once in a COLUMN
    // if that's the only place in the column it COULD go, then that's where it MUST go
    loop through all the columns
        loop through all the numbers (1 to 9)
            if there's only one place it can be
                setCell()
                recursively attemptToSolve()
}

function test2s()
{
    // finds where a number is only possible once in a SQUARE
    // if that's the only place in the square it COULD go, then that's where it MUST go
}

function test3r()
{
    // Looks for sets of two possibles in a row
    // then will remove those digits from other possibles along the same row
}

function test3c()
{
    // Looks for sets of two possibles in a column,
    // then will remove those digits from other possibles along the same column
}

function test4r()
{
    // Looks for sets of 3 possibles that match in a row,
    // then will remove possibles along the same row
    // Will also match a set of 3, set of 3 and set of 2
    // eg. "156", "15", "156 would be a match and remove 1, 5, & 6 from the other possibles
}

function test4c()
{
    // Looks for sets of 3 possibles that match in a column,
    // then will remove possibles along the same column
    // Will also match a set of 3, set of 3 and set of 2
    // eg. "156", "15", "156 would be a match and remove 1, 5, & 6 from the other possibles
}

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