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1 Answer
Ankith Reddy
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This algorithm is used to print the array elements in a spiral way. At first starting from the first row, print the whole content and then follow the last column to print, then the last row and so on, thus it prints the elements in spiral fashion. 

The time complexity of this algorithm is O(MN), M is the number of rows and N is the number of columns.

Input and Output

Input:
The matrix:
 1   2   3   4   5   6
 7   8   9  10  11  12
13  14  15  16  17  18

Output:
Contents of an array as the spiral form
1 2 3 4 5 6 12 18 17 16 15 14 13 7 8 9 10 11 15 16

Algorithm

dispSpiral(mat, m, n)

Input: The matrix mat, row and column m and n.

Output: Print the elements of the matrix in a spiral way.

Begin
   currRow := 0 and currCol := 0
   while currRow and currCol are in the matrix range, do
      for i in range currCol and n-1, do
         display mat[currRow, i]
      done

      increase currRow by 1
      for i in range currRow and m-1, do
         display mat[i, n-1]
      done

      decrease n by 1
      if currRow < m, then
         for i := n-1 down to currCol, do
            display mat[m-1, i]
         done
         decrease m by 1
      if currCol < n, then
         for i := m-1 down to currRow, do
            display mat[i, currCol]
         done
         increase currCol by 1
   done
End

Source Code (C++)

#include <iostream>
#define ROW 3
#define COL 6
using namespace std;

int array[ROW][COL] = {
   {1, 2, 3, 4, 5, 6},
   {7, 8, 9, 10, 11, 12},
   {13, 14, 15, 16, 17, 18}
};

void dispSpiral(int m, int n) {
   int i, currRow = 0, currCol = 0;
   while (currRow < ROW && currCol <COL) {
      for (i = currCol; i < n; i++) {          //print the first row normally
         cout << array[currRow][i]<<" ";
      }
      currRow++;           //point to next row

      for (i = currRow; i < m; ++i) {       //Print the last column
         cout << array[i][n-1]<<" ";
      }

      n--;               //set the n-1th column is current last column

      if ( currRow< m) {         //when currRow is in the range, print the last row
         for (i = n-1; i >= currCol; --i) {
            cout << array[m-1][i]<<" ";
         }
         m--; //decrease the row range
      }

      if (currCol <n) {      //when currCol is in the range, print the fist column
         for (i = m-1; i >= currRow; --i) {
            cout << array[i][currCol]<<" ";
         }
         currCol++;
      }
   }
}

int main() {
   dispSpiral(ROW, COL);
}

Output

1 2 3 4 5 6 12 18 17 16 15 14 13 7 8 9 10 11 15 16
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