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
Javascript
<script> // This is a modified code of // print-a-given-matrix-in-spiral-form/ let R = 3; let C = 6; // Function that print matrix in // reverse spiral form. function ReversespiralPrint(m, n, a)
{ // Large array to initialize it
// with elements of matrix
let b = new Array(100);
/* k - starting row index
l - starting column index*/
let i, k = 0, l = 0;
// Counter for single dimension array
//in which elements will be stored
let z = 0;
// Total elements in matrix
let size = m*n;
while (k < m && l < n)
{
// Variable to store value of matrix.
let val;
/* Print the first row from
the remaining rows */
for (i = l; i < n; ++i)
{
// printf("%d ", a[k][i]);
val = a[k][i];
b[z] = val;
++z;
}
k++;
/* Print the last column from
the remaining columns */
for (i = k; i < m; ++i)
{
// printf("%d ", a[i][n-1]);
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)
{
// printf("%d ", a[m-1][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)
{
// printf("%d ", a[i][l]);
val = a[i][l];
b[z] = val;
++z;
}
l++;
}
}
for (let i=size-1 ; i>=0 ; --i)
{
document.write(b[i] + " " );
}
} /* Driver program to test above functions */ let a = [ [1, 2, 3, 4, 5, 6],
[7, 8, 9, 10, 11, 12],
[13, 14, 15, 16, 17, 18]];
ReversespiralPrint(R, C, a);
</script> |
Output:
11 10 9 8 7 13 14 15 16 17 18 12 6 5 4 3 2 1
Time complexity: O(R*C) where R and C are no of rows and columns in given matrix
Auxiliary Space: O(1) because using constant space
Please refer complete article on Print a given matrix in reverse spiral form for more details!