2d Array in Spiral Order

Question

I'm trying to fill an array in spiral order. So far, I can print the array in spiral order, but is there a way to modify the array so that i can fill it in spiral order and then just print the array? I'd like it to go in decreasing order like a countdown. Please help!

public class Spiral {
  public static void main(int m, int n) { 

    // create m by n array of integers 1 through m*n
    int[][] values = new int[m][n];
    for (int i = 0; i < m; i++)
        for (int j = 0; j < n; j++)
            values[i][j] = 1 + (m*n)*i + j;

    // spiral
    for (int i = (m*n)-1, j = 0; i > 0; i--, j++) {
          for (int k = j; k < i; k++) System.out.println(values[j][k]);
          for (int k = j; k < i; k++) System.out.println(values[k][i]);
          for (int k = i; k > j; k--) System.out.println(values[i][k]);
          for (int k = i; k > j; k--) System.out.println(values[k][j]);
    }
  }
}

Answer 1

Below function is a square matrix with a size N × N containing integers from 1 to N * N in a spiral order, starting from top-left and in clockwise direction.

int[][] spiralNumbers(int n) {
int[][] matrix = new int[n][n];
for (int step = 0, a = 0, size; step < n/2; step++) {
    size = (n - step * 2 - 1);
    for (int i = 0, chunk, chunkIndex, chunkOffset; i < 4 * size; i++) {
        chunk = i / size;
        chunkIndex = i % size;
        chunkOffset = n - step - 1;
        switch (chunk) {
            case 0:
                matrix[step][chunkIndex + step] = a+1;
                break;
            case 1:
                matrix[chunkIndex + step][chunkOffset] = a+1;
                break;
            case 2:
                matrix[chunkOffset][chunkOffset - chunkIndex] = a+1;
                break;
            case 3:
                matrix[chunkOffset - chunkIndex][step] = a+1;
                break;
            default:
                throw new IndexOutOfBoundsException();
        }
        a++;
    }
    if (n % 2 == 1) {
        matrix[n/2][n/2] = n * n;
    }
}
return matrix; 
}

Answer 2

int maxValue = target.length * target[0].length;

private int[][] generateMatrix(int[][] target, int level, int currentVal) {
    // always start from lower left corner in each layer
    int w = level;
    int h = target.length - level - 1;

    // fill the bottom line
    int i = 0;
    for (i = w; i < target[0].length - level && currentVal <= maxValue; i++) {
        target[h][i] = currentVal++;
    }

    w = target[0].length - level - 1;

    int j = 0;
    // fill the right line
    for (j = h - 1; j >= level && currentVal <= maxValue; j--) {
        target[j][w] = currentVal++;
    }

    h = level;

    // fill the above line
    for (i = w - 1; i >= level && currentVal <= maxValue; i--) {
        target[h][i] = currentVal++;
    }
    w = level;

    // fill the left line
    for (j = h + 1; j < target.length - level - 1 && currentVal <= maxValue; j++) {
        target[j][w] = currentVal++;
    }

    if (currentVal > maxValue)
        return target;
    return generateMatrix(target, ++level, currentVal);

}

Answer 3

Here is some of the variations:

public class SpiralMatrix {

    private static int[][] createSpiralMatrix(int size) {
        int[][] matrix = new int[size][size];

        int row = 0, col = -1;
        int value = 1;

        boolean horizontal = true;
        boolean increasing = true;
        boolean finish = false;

        while(!finish) {

            finish = true;
            if (horizontal && increasing) {
                while(tryAndSet(matrix, row, col + 1, value)) {
                    finish = false;
                    col++;
                    value++;
                }
            } else if (horizontal && !increasing) {
                while(tryAndSet(matrix, row, col - 1, value)) {
                    finish = false;
                    col--;
                    value++;
                }
            } else if (!horizontal && increasing) {
                while(tryAndSet(matrix, row + 1, col, value)) {
                    finish = false;
                    row++;
                    value++;
                }
            } else {
                while(tryAndSet(matrix, row - 1, col, value)) {
                    finish = false;
                    row--;
                    value++;
                }
            }

            if (!horizontal) {
                increasing = !increasing;
            }
            horizontal = !horizontal;
        }

        return matrix;
    }


    private static boolean tryAndSet(int[][] matrix, int row, int col, int value) {
        if (row < 0 || col < 0 || row >= matrix.length || col >= matrix[row].length || matrix[row][col] != 0) {
            return false;
        }
        matrix[row][col] = value;
        return true;
    }

    private static void printMatrix(int[][] matrix) {
        for (int i = 0; i < matrix.length; i++) {
            for(int j = 0; j < matrix[i].length; j++) {
                System.out.print("\t" + matrix[i][j]);
            }
            System.out.println();
        }
    }


    public static void main(String[] args) {
        try {
            int[][] spiralMatrix = createSpiralMatrix(40);
            printMatrix(spiralMatrix);
        } catch (Throwable th) {
            th.printStackTrace();
        }
    }

Answer 4

public ArrayList<Integer> spiralOrder(final List<ArrayList<Integer>> a) {
     ArrayList<Integer> result = new ArrayList<Integer>();
      int m = a.get(0).size();
      int n = a.size();
      if(m>1 && n>1){
         int loopCounter = (n > m)  ? m*2 : n *2 -1 ;
         int opr=1;
         int i=0,j=0;
         int opA=m,opB=n,opC=0,opD=1;
         for(int k=0;k < loopCounter ;k++){
              if(opr == 1){
                 int counter =0;
                 while(counter < opA){
                    System.out.print(a.get(i).get(j)+ ";");
                    result.add(a.get(i).get(j));
                    counter++;

                    if(j != opA-1){
                        j++;
                    }
                    else{
                        break;
                    }
                 }
                 opr =2;
                 continue;
             }
             if(opr == 2){
                 i++;
                 int counter =1;
                 while(counter < opB){
                     System.out.print(a.get(i).get(j)+ ";");
                    result.add(a.get(i).get(j));
                    counter++;

                   if( i != opB-1){
                     i++;
                   }
                   else{
                       break;
                   }
                 }
                 opr =3;
                 continue;
             }
             if(opr == 3){
                 j--;
                 int counter =j;
                 while(counter >= opC){
                     System.out.print(a.get(i).get(j)+ ";");
                    result.add(a.get(i).get(j));
                    counter --;
                     if(j != opC){
                     j--;
                    }
                    else{
                        break;
                    }
                  }
                 opr =4;
                 continue;
             }
             if(opr == 4){
                 i--;
                 int counter = i;
                 while(counter >= opD){
                     System.out.print(a.get(i).get(j)+ ";");
                    result.add(a.get(i).get(j));
                    counter --;
                    if(i != opD){
                     i--;
                    }else{
                        break;
                    }
                 }
                 opr =1;
                 j++;
                 opA = opA -1;
                 opB = opB -1;
                 opC= opC +1;
                 opD = opD+1;
                 continue;
             }
         }

     }

         else if(n ==1){
              for(int k=0;k < a.get(0).size();k++){
                  result.add(a.get(0).get(k));
              }
         }

       else if(m==1 && n==1){
             result.add(a.get(0).get(0));
         }

     // Populate result;
     return result;

}

Answer 5

Here's my take on this:

public class SpiralMatrix {
public static void main(String[] args) {
    int[][] matrix = new int[5][5];
    int startRow = 0;
    int endRow = matrix.length - 1;
    int startCol = 0;
    int endCol = matrix.length - 1;
    int counter = 1;
    int cycleEnder = matrix.length * matrix.length;


    while (counter <= cycleEnder) {

        //FIRST ROW
        for (int i = 0; i <= endCol; i++) {
            matrix[startRow][i] = counter;
            counter++;
        }
        startRow++;
        //RIGHT-SIDE COL
        for (int i = startRow; i <= endRow; i++) {
            matrix[i][endCol] = counter;
            counter++;
        }
        endCol--;
        //BOTTOM ROW REVERSE
        for (int i = endCol; i >= startCol; i--) {
            matrix[endRow][i] = counter;
            counter++;
        }
        endRow--;

        //FIRST COL UP
        for (int i = endRow; i > startRow; i--) {
            matrix[i][startCol] = counter;
            counter++;
        }
        startCol++;


    }
    for (int[] ints : matrix) {
        for (int j = 0; j < matrix.length; j++) {
            if (ints[j] < 10) {
                System.out.print(ints[j] + "  ");
            } else {
                System.out.print(ints[j] + " ");
            }

        }
        System.out.println();
    }
}


    public static void showMatrix ( int[][] mat, int x, int y){
        for (int i = 0; i < mat.length; i++) {
            for (int j = 0; j < mat.length; j++) {
                System.out.print(mat[i][j] + " ");
            }
            System.out.println();
        }
    }
}

Answer 6

If you've figured out code to do the reads (for printing), then surely you can just modify that to do writes instead, using the same logic?

If you want each cell in the matrix to contain its "sequential number", counting backwards, something like this ought to work, assuming your access logic is correct:

for (int i = (m*n)-1, j = 0, index = m * n; i > 0; i--, j++) {
      for (int k = j; k < i; k++) values[j][j] = index--;
      for (int k = j; k < i; k++) values[k][i] = index--;
      for (int k = i; k > j; k--) values[i][k] = index--;
      for (int k = i; k > j; k--) values[k][j] = index--;
}

Answer 7

Not the most efficient, but it should work: g is the array. I'm also using exceptions to control logic.

public static void spiralFill()
{
    x = (g.length-1)/2;
    y = (g[0].length-1)/2;

    try
    {
        while(true)
        {
             east();
             south();
             step++;
             west();
             north();
             step++;        
        }
    }
    catch(ArrayIndexOutOfBoundsException e)
    {

    }
}

public static void east()
{
for(int i = 0; i < step; i++)
{
        g[x][y] = count;
        count++;
    x++;
    }
}
public static void south()
{
    for(int i = 0; i < step; i++)
    {
        g[x][y] = count;
        count++;
        y--;
    }
}   
public static void west()
{
    for(int i = 0; i < step; i++)
    {
         g[x][y] = count;
         count++;
         x--;
    }
}   
public static void north()
{
   for(int i = 0; i < step; i++)
   {
       g[x][y] = count;
       count++;
       y++;
   }
}