Moving elements in array

Question

I am trying to move the false element in 2d array to a different blank space in element

'X*''O'' ''X''O*'
'O''O'' '' ''X'
'O'' ''X''X''O*'
'X'' '' ''X''X'
'X''X''O*''X''O*'

the elements marked with * are false elements. I want to move those false cells to look like this. In other word move all the false elements to blank space in the array

' ''O''X''X'' '
'O''O''O'' ''X'
'O''O''X''X'' '
'X''O''O''X''X'
'X''X'' ''X'' '

This is what I have so far but not getting the result, it only moves one element not all the false elements. And when I try to put break in outer loop it does not work. Any tips please, this is my code so far:

char temp = ' ';
char[][] arr = new char[tissue.length][tissue[0].length];
for (int i = 0; i < tissue.length; i++)
    for (int j = 0; j < tissue[i].length; j++){
        if (isSatisfied(tissue, i, j, threshold)
            arr[i][j] = tissue[i][j];
        if ( !isSatisfied(tissue, i, j, threshold)) {
            temp = tissue[i][j];
            breakloop:
            for (int k = 0; k < tissue.length; k++)
                for (int l = 0; l < tissue[k].length; l++)
                    if (tissue[k][l] == ' ') {
                        tissue[i][j] = arr[k][l];
                        arr[k][l] = temp;
                        break breakloop;
                    }
        }
    }

Why do you create a whole new array? Why not modify the array to change the false elements to blanks? — CBredlow
– CBredlow, Commented Nov 20, 2014 at 6:50
One question, how are the new locations for the false values choosen? Closest space? or filling the array from the start? or some other way? — Eric
– Eric, Commented Nov 20, 2014 at 7:34

Eric · Accepted Answer · 2014-11-20 14:18:19Z

Here is a working solution. The processing is done over a single array, because it's easier to handle.

public class MoveArrayValues
{
    final static String F = "X*", E = "O*";
    final static String X = "X", O = "O";
    final static String B = " ", T = "-";

    final static int COLUMN_COUNT = 5;

    public static void main( String[] args )
    {
        String[] source = 
            { 
                F, O, B, X, E, 
                O, O, B, B, X,
                O, B, X, X, E, 
                X, B, B, X, X, 
                X, X, E, X, E
            };

        // Print the original source
        for ( int ptr = 0; ptr < source.length; ptr++ )
        {
            System.out.print("[" + source[ptr] + "]");
            if ( ptr != 0 && ((ptr + 1) % COLUMN_COUNT) == 0 ) System.out.println();
        }

        // Initialise the target array and then process the source
        String[] target = new String[source.length];
        for ( int ptr = 0; ptr < source.length; ptr++ )
        {
            String cell = source[ptr];
            if ( cell.equals(T) )
            { // Skip cells marked as "taken"
                continue;
            }
            if ( cell.equals(F) || cell.equals(E) )
            { // False values
                target[ptr] = B; // false value becomes a blank

                // now find a new location for this false value
                int offset = 1;
                /*
                 * This while loop will find the closest free cell that
                 * hasn't already been taken (preferring the cell to the
                 * right).
                 * 
                 * The while condition is just to make sure we don't 
                 * fall into an endless loop
                 */
                while ( offset < source.length )
                {
                    if ( ptr + offset < source.length )
                    { // Scan to the right
                        String tmp = source[ptr + offset];
                        if ( tmp.equals(B) )
                        { // found a blank, now use this space
                            source[ptr + offset] = T; // Mark the space as "taken"
                            target[ptr + offset] = cell.equals(F) ? X : O;
                            break;
                        }
                    }
                    if ( ptr - offset >= 0 )
                    { // Scan to the left
                        String tmp = source[ptr - offset];
                        if ( tmp.equals(B) )
                        { // found a blank, now use this space
                            source[ptr - offset] = T; // Mark the space as "taken"
                            target[ptr - offset] = cell.equals(F) ? X : O;
                            break;
                        }
                    }
                    offset++;
                }
            }
            else
            { // Normal values and spaces
                target[ptr] = cell;
            }
        }

        System.out.println("--------------------");
        // Print the resultant target
        for ( int ptr = 0; ptr < target.length; ptr++ )
        {
            System.out.print("[" + target[ptr] + "]");
            if ( ptr != 0 && ((ptr + 1) % COLUMN_COUNT) == 0 ) System.out.println();
        }
    }
}

If you really need to work with 2d arrays, then you could either modify the outer for loop and inner while loop or even easier, write a little method to convert the 2d array into a single array, which is very easy.

you overcomplicated things, it would have been sufficient just to copy and replace the values in the new array String[] target = new String[source.length]; for (int i = 0; i < source.length; i++) { if (source[i].equals(F) || source[i].equals(E)) { target[i] = B; } else { target[i] = source[i]; } }
@MihaiC, how does your simplified code move the false value to a new location?
you are right, i misread the question. assumed op only wanted to replace false values.

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