Print matrix in antispiral form

Given a 2D array, the task is to print matrix in anti spiral form:

Examples:

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

Input : arr[][4] = {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 :arr[][6] = {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

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

The idea is simple, we traverse matrix in spiral form and put all traversed elements in a stack. Finally one by one elements from stack and print them.

C++

// C++ program to print matrix in anti-spiral form 
#include <bits/stdc++.h> 
using namespace std; 
#define R 4 
#define C 5 
  
void antiSpiralTraversal(int m, int n, int a[R][C]) 
{ 
    int i, k = 0, l = 0; 
  
    /*  k - starting row index 
        m - ending row index 
        l - starting column index 
        n - ending column index 
        i - iterator  */
    stack<int> stk; 
  
    while (k <= m && l <= n) 
    { 
        /* Print the first row from the remaining rows */
        for (i = l; i <= n; ++i) 
            stk.push(a[k][i]); 
        k++; 
  
        /* Print the last column from the remaining columns */
        for (i = k; i <= m; ++i) 
            stk.push(a[i][n]); 
        n--; 
  
        /* Print the last row from the remaining rows */
        if ( k <= m) 
        { 
            for (i = n; i >= l; --i) 
                stk.push(a[m][i]); 
            m--; 
        } 
  
        /* Print the first column from the remaining columns */
        if (l <= n) 
        { 
            for (i = m; i >= k; --i) 
                stk.push(a[i][l]); 
            l++; 
        } 
    } 
  
    while (!stk.empty()) 
    { 
        cout << stk.top() << " "; 
        stk.pop(); 
    } 
} 
  
/* Driver program to test above functions */
int main() 
{ 
    int mat[R][C] = 
    { 
        {1,  2,  3,  4,  5}, 
        {6,  7,  8,  9,  10}, 
        {11, 12, 13, 14, 15}, 
        {16, 17, 18, 19, 20} 
    }; 
  
    antiSpiralTraversal(R-1, C-1, mat); 
  
    return 0; 
} 

Java

// Java Code for Print matrix in antispiral form 
import java.util.*; 
  
class GFG { 
      
    public static void antiSpiralTraversal(int m, int n,  
                                             int a[][]) 
    { 
        int i, k = 0, l = 0; 
       
        /*  k - starting row index 
            m - ending row index 
            l - starting column index 
            n - ending column index 
            i - iterator  */
        Stack<Integer> stk=new Stack<Integer>(); 
       
        while (k <= m && l <= n) 
        { 
            /* Print the first row from the remaining  
             rows */
            for (i = l; i <= n; ++i) 
                stk.push(a[k][i]); 
            k++; 
       
            /* Print the last column from the remaining 
            columns */
            for (i = k; i <= m; ++i) 
                stk.push(a[i][n]); 
            n--; 
       
            /* Print the last row from the remaining  
            rows */
            if ( k <= m) 
            { 
                for (i = n; i >= l; --i) 
                    stk.push(a[m][i]); 
                m--; 
            } 
       
            /* Print the first column from the remaining  
            columns */
            if (l <= n) 
            { 
                for (i = m; i >= k; --i) 
                    stk.push(a[i][l]); 
                l++; 
            } 
        } 
       
        while (!stk.empty()) 
        { 
            System.out.print(stk.peek() + " "); 
            stk.pop(); 
        } 
    } 
      
    /* Driver program to test above function */
    public static void main(String[] args)  
    { 
         int mat[][] = 
                { 
                    {1,  2,  3,  4,  5}, 
                    {6,  7,  8,  9,  10}, 
                    {11, 12, 13, 14, 15}, 
                    {16, 17, 18, 19, 20} 
                }; 
               
        antiSpiralTraversal(mat.length - 1, mat[0].length - 1,  
                                                       mat); 
    } 
  } 
// This code is contributed by Arnav Kr. Mandal. 

Python 3

# Python 3 program to print 
# matrix in anti-spiral form 
R = 4
C = 5
  
def antiSpiralTraversal(m, n, a): 
    k = 0
    l = 0
  
    # k - starting row index 
    # m - ending row index 
    # l - starting column index 
    # n - ending column index 
    # i - iterator  
    stk = [] 
  
    while (k <= m and l <= n): 
          
        # Print the first row  
        # from the remaining rows  
        for i in range(l, n + 1): 
            stk.append(a[k][i]) 
        k += 1
  
        # Print the last column  
        # from the remaining columns  
        for i in range(k, m + 1): 
            stk.append(a[i][n]) 
        n -= 1
  
        # Print the last row 
        # from the remaining rows  
        if ( k <= m): 
            for i in range(n, l - 1, -1): 
                stk.append(a[m][i]) 
            m -= 1
  
        # Print the first column  
        # from the remaining columns  
        if (l <= n): 
            for i in range(m, k - 1, -1): 
                stk.append(a[i][l]) 
            l += 1
          
    while len(stk) != 0: 
        print(str(stk[-1]), end = " ") 
        stk.pop() 
  
# Driver Code 
mat = [[1, 2, 3, 4, 5], 
       [6, 7, 8, 9, 10], 
       [11, 12, 13, 14, 15], 
       [16, 17, 18, 19, 20]]; 
  
antiSpiralTraversal(R - 1, C - 1, mat) 
  
# This code is contributed 
# by ChitraNayal 

C#

using System; 
using System.Collections.Generic; 
  
// C# Code for Print matrix in antispiral form  
  
public class GFG 
{ 
  
    public static void antiSpiralTraversal(int m, int n, int[][] a) 
    { 
        int i, k = 0, l = 0; 
  
        /*  k - starting row index  
            m - ending row index  
            l - starting column index  
            n - ending column index  
            i - iterator  */
        Stack<int> stk = new Stack<int>(); 
  
        while (k <= m && l <= n) 
        { 
            /* Print the first row from the remaining   
             rows */
            for (i = l; i <= n; ++i) 
            { 
                stk.Push(a[k][i]); 
            } 
            k++; 
  
            /* Print the last column from the remaining  
            columns */
            for (i = k; i <= m; ++i) 
            { 
                stk.Push(a[i][n]); 
            } 
            n--; 
  
            /* Print the last row from the remaining   
            rows */
            if (k <= m) 
            { 
                for (i = n; i >= l; --i) 
                { 
                    stk.Push(a[m][i]); 
                } 
                m--; 
            } 
  
            /* Print the first column from the remaining   
            columns */
            if (l <= n) 
            { 
                for (i = m; i >= k; --i) 
                { 
                    stk.Push(a[i][l]); 
                } 
                l++; 
            } 
        } 
  
        while (stk.Count > 0) 
        { 
            Console.Write(stk.Peek() + " "); 
            stk.Pop(); 
        } 
    } 
  
    /* Driver program to test above function */
    public static void Main(string[] args) 
    { 
         int[][] mat = new int[][] 
         { 
             new int[] {1, 2, 3, 4, 5}, 
             new int[] {6, 7, 8, 9, 10}, 
             new int[] {11, 12, 13, 14, 15}, 
             new int[] {16, 17, 18, 19, 20} 
         }; 
  
        antiSpiralTraversal(mat.Length - 1, mat[0].Length - 1, mat); 
    } 
} 
  
// This code is contributed by Shrikant13 

Output:

12 13 14 9 8 7 6 11 16 17 18 19 20 15 10 5 4 3 2 1

This article is contributed by DANISH_RAZA. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

Don’t stop now and take your learning to the next level. Learn all the important concepts of Data Structures and Algorithms with the help of the most trusted course: DSA Self Paced. Become industry ready at a student-friendly price.

My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python 3

C#

Recommended Posts: