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 formclass 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!
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