Given a 2D array, print it in reverse spiral form. We have already discussed Print a given matrix in spiral form. This article discusses how to do the reverse printing. See the following examples.
Input: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Output: 10 11 7 6 5 9 13 14 15 16 12 8 4 3 2 1 Input: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Output: 11 10 9 8 7 13 14 15 16 17 18 12 6 5 4 3 2 1
Java
// JAVA Code for Print a given matrix in // reverse spiral form class GFG {
public static int R = 3 , C = 6 ;
// Function that print matrix in reverse spiral form.
public static void ReversespiralPrint( int m, int n,
int a[][])
{
// Large array to initialize it
// with elements of matrix
long b[] = new long [ 100 ];
/* k - starting row index
l - starting column index*/
int i, k = 0 , l = 0 ;
// Counter for single dimension array
//in which elements will be stored
int z = 0 ;
// Total elements in matrix
int size = m * n;
while (k < m && l < n)
{
// Variable to store value of matrix.
int val;
/* Print the first row from the remaining
rows */
for (i = l; i < n; ++i)
{
val = a[k][i];
b[z] = val;
++z;
}
k++;
/* Print the last column from the remaining
columns */
for (i = k; i < m; ++i)
{
val = a[i][n- 1 ];
b[z] = val;
++z;
}
n--;
/* Print the last row from the remaining
rows */
if ( k < m)
{
for (i = n- 1 ; i >= l; --i)
{
val = a[m- 1 ][i];
b[z] = val;
++z;
}
m--;
}
/* Print the first column from the remaining
columns */
if (l < n)
{
for (i = m- 1 ; i >= k; --i)
{
val = a[i][l];
b[z] = val;
++z;
}
l++;
}
}
for ( int x = size- 1 ; x>= 0 ; --x)
{
System.out.print(b[x]+ " " );
}
}
/* Driver program to test above function */
public static void main(String[] args)
{
int a[][] = { { 1 , 2 , 3 , 4 , 5 , 6 },
{ 7 , 8 , 9 , 10 , 11 , 12 },
{ 13 , 14 , 15 , 16 , 17 , 18 }};
ReversespiralPrint(R, C, a);
}
}
// This code is contributed by Arnav Kr. Mandal. |
Output:
11 10 9 8 7 13 14 15 16 17 18 12 6 5 4 3 2 1
Time complexity: O(m*n) where m is no of rows and n is no of columns of a given matrix
Auxiliary Space: O(1) as using constant space
Please refer complete article on Print a given matrix in reverse spiral form for more details!