Print Matrix in Spiral order using Recursion.

Print Matrix in Spiral order OR
Given m*n matrix(m rows, n columns), print all elements of the matrix in spiral order OR
Print two-dimensional array in spiral order OR
How to print elements of Matrix in Spiral Format?

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Given a Matrix(2D array), print it in spiral form. Lets understand the problem statement graphically and it will be more clear,  

Algorithm

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There are 2 ways to print matrix in Spiral order. 

1. Iterative.
2. Recursive.

In case if you like to visit all questions related to Matrix on our blog,

1. Top 10 Matrix Interview Questions in Java.
2. Print Matrix in Spiral order iteratively.
3. Rotate Matrix by 90 degrees clockwise Inplace

In this post, we will focus on Recursive approach.

In Iterative approach, we need to maintain 4 variables rowStart, rowLength, colStart, colLength which help in printing matrix in Spiral way.
 

Next recursive call will use this 4 variables as reference for identifying start of matrix row, matrix row length, start of matrix column, and matrix column length. It continues till all layers are printed.

You can compare Printing Matrix in Spiral form to Peeling an onion.

First, you peel off the outer-layer skin (Print outer matrix). After the first layer is peeled off, there’s another layer to peel (Print inner matrix).

So you peel off the remaining onion again until there is no more to peel, which is where you stop.
(In our case we stop when rowStart meets rowLength or colStart meets colLength).

Java Program to Print Matrix in Spiral order using Recursion

package javabypatel.matrix;

public class PrintMatrixInSpiralForm {

 public static void main(String[] args) {
  new PrintMatrixInSpiralForm();
 }

 public PrintMatrixInSpiralForm() {
  int[][] matrix = {
   {1,4,7,10},
   {2,5,8,11}
  };
  
  printMatrixInSpiralWayUsingRecursion(matrix,0,0,matrix[0].length-1,matrix.length-1);
 }
 
 private void printMatrixInSpiralWayUsingRecursion(int[][] matrix, int rowStart, int colStart, int colLength,  int rowLength){
  for (int i = rowStart; i <= colLength; i++) {
   System.out.print(matrix[rowStart][i] + " ");
  }
  for (int i = rowStart+1; i <= rowLength; i++) {
   System.out.print(matrix[i][colLength] + " ");
  }
  
  if(rowStart+1 <= rowLength){
   for (int i = colLength-1; i >= colStart; i--) {
    System.out.print(matrix[rowLength][i] + " ");
   } 
  }
  
  if(colStart+1 <= colLength){
   for (int i = rowLength-1; i > rowStart; i--) {
    System.out.print(matrix[i][colStart] + " ");
   }
  }
  
  if(rowStart+1 <= rowLength-1 && colStart+1 <= colLength-1){
   printMatrixInSpiralWayUsingRecursion(matrix, rowStart+1, colStart+1, colLength-1, rowLength-1);
  }
 }
}

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