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Print a matrix in Reverse Wave Form
  • Difficulty Level : Easy
  • Last Updated : 04 Jul, 2018

Given a matrix, print it in Reverse Wave Form.

Examples :

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

Input :  1  9  4  10
         3  6  90 11
         2  30 85 72
         6  31 99 15 
Output : 10 11 72 15 99 85 90 4 9 6 30 31 6 2 3 1

Approach :To get the reverse wave form for a given matrix, we first print the elements of the last column of the matrix in downward direction then print the elements of the 2nd last column in the upward direction, then print the elements in third last column in downward direction and so on. For example 1, the flow goes like :
matrix-reverse-wave-form

Below is the implementation to print reverse wave form of a matrix :

C++




// C++ implementation to print
// reverse wave form of matrix
#include<bits/stdc++.h>
using namespace std;
  
#define R 4
#define C 4
  
// function to print reverse wave 
// form for a given matrix
void WavePrint(int m, int n, int arr[R][C])
{
    int i, j = n - 1, wave = 1;
  
    /* m     - Ending row index
        n     - Ending column index
        i, j     - Iterator
        wave     - for Direction
        wave = 1 - Wave direction down
        wave = 0 - Wave direction up   */
    while (j >= 0) {
          
        // Check whether to go in
        // upward or downward
        if (wave == 1) {
              
            // Print the element of the matrix
            // downward since the value of wave = 1
            for (i = 0; i < m; i++) 
                cout << arr[i][j] << " ";  
            
            wave = 0;
            j--;
        }
        else {
              
            // Print the elements of the 
            // matrix upward since the value
            // of wave = 0
            for (i = m - 1; i >= 0; i--) 
                cout << arr[i][j] << " ";
              
            wave = 1;
            j--;
        }
    }
}
  
// driver function
int main()
{
    int arr[R][C] = { { 1, 2, 3, 4 },
                      { 5, 6, 7, 8 },
                      { 9, 10, 11, 12 },
                      { 13, 14, 15, 16 } };                    
    WavePrint(R, C, arr);
      
    return 0;
}


Java




// Java implementation to print
// reverse wave form of matrix
import java.io.*;
  
class GFG 
{
    static int R = 4;
    static int C = 4;
      
    // function to print reverse wave 
    // form for a given matrix
    static void WavePrint(int m, int n, int arr[][])
    {
        int i, j = n - 1, wave = 1;
      
        // m- Ending row index
        //n - Ending column index
        //i, j     - Iterator
        //wave     - for Direction
        //wave = 1 - Wave direction down
        //wave = 0 - Wave direction up */
        while (j >= 0
        {
              
            // Check whether to go in
            // upward or downward
            if (wave == 1
            {
                // Print the element of the matrix
                // downward since the value of wave = 1
                for (i = 0; i < m; i++) 
                    System.out.print(arr[i][j] +" "); 
              
                wave = 0;
                j--;
            }
            else {
                  
                // Print the elements of the 
                // matrix upward since the value
                // of wave = 0
                for (i = m - 1; i >= 0; i--) 
                    System.out.print( arr[i][j] + " ");
                  
                wave = 1;
                j--;
            }
        }
    }
      
    // Driver function
    public static void main (String[] args) 
    {
        int arr[][] = { { 1, 2, 3, 4 },
                    { 5, 6, 7, 8 },
                    { 9, 10, 11, 12 },
                    { 13, 14, 15, 16 } };             
        WavePrint(R, C, arr);   
      
    }
}
  
// This code is contributed by vt_m


Python3




# Python3 implementation to print
# reverse wave form of matrix
  
R = 4
C = 4
  
# function to print reverse wave 
# form for a given matrix
def wavePrint(m, n, arr):
    j = n - 1
    wave = 1
      
    # m     - Ending row index
    # n     - Ending column index
    # i, j     - Iterator
    # wave     - for Direction
    # wave = 1 - Wave direction down
    # wave = 0 - Wave direction up 
    while j >= 0:
          
        # Check whether to go in
        # upward or downward
        if wave == 1:
      
            # Print the element of the 
            # matrix downward since the
                        # value of wave = 1
            for i in range(m):
                print(arr[i][j], end = " "),
            wave = 0
            j -= 1
              
              
        else:
            # Print the elements of the 
            # matrix upward since the 
            # value of wave = 0
            for i in range(m - 1, -1, -1):
                print(arr[i][j], end = " "),
                  
            wave = 1
            j -= 1
  
# Driver code
arr = [ [ 1, 2, 3, 4 ],
        [ 5, 6, 7, 8 ],
        [ 9, 10, 11, 12 ],
        [ 13, 14, 15, 16 ] ]
          
wavePrint(R, C, arr)
  
# This code is contributed by 
# Upendra Singh Bartwal


C#




// C# implementation to print
// reverse wave form of matrix
using System;
  
class GFG {
      
    static int R = 4;
    static int C = 4;
      
    // function to print reverse wave 
    // form for a given matrix
    static void WavePrint(int m, int n, int [,]arr)
    {
          
        int i, j = n - 1, wave = 1;
      
        // m- Ending row index
        // n - Ending column index
        // i, j - Iterator
        // wave - for Direction
        // wave = 1 - Wave direction down
        // wave = 0 - Wave direction up */
        while (j >= 0) 
        {
              
            // Check whether to go in
            // upward or downward
            if (wave == 1) {
                  
                // Print the element of the 
                // matrix downward since the
                // value of wave = 1
                for (i = 0; i < m; i++) 
                    Console.Write(arr[i,j] + " "); 
              
                wave = 0;
                j--;
            }
              
            else {
                  
                // Print the elements of the 
                // matrix upward since the value
                // of wave = 0
                for (i = m - 1; i >= 0; i--) 
                    Console.Write( arr[i,j] + " ");
                  
                wave = 1;
                j--;
            }
        }
    }
      
    // Driver function
    public static void Main () 
    {
        int [,]arr = { { 1, 2, 3, 4 },
                       { 5, 6, 7, 8 },
                       { 9, 10, 11, 12 },
                       { 13, 14, 15, 16 } };
                         
        WavePrint(R, C, arr); 
      
    }
}
  
// This code is contributed by vt_m.


PHP




<?php
// PHP implementation to print
// reverse wave form of matrix
$R = 4;
$C = 4;
  
// function to print reverse 
// wave form for a given matrix
function WavePrint($m, $n, $arr)
{
    global $R;
    global $C;
  
    $i; $j = $n - 1; $wave = 1;
  
    /*  m - Ending row index
        n - Ending column index
        i, j     - Iterator
        wave     - for Direction
        wave = 1 - Wave direction down
        wave = 0 - Wave direction up */
    while ($j >= 0) 
    {
          
        // Check whether to go in
        // upward or downward
        if ($wave == 1) 
        {
              
            // Print the element of the 
            // matrix downward since the 
            // value of wave = 1
            for ($i = 0; $i < $m; $i++) 
                echo $arr[$i][$j] , " "
          
            $wave = 0;
            $j--;
        }
        else 
        {
              
            // Print the elements of 
            // the matrix upward since
            // the value of wave = 0
            for ($i = $m - 1; $i >= 0; $i--) 
                echo $arr[$i][$j] , " ";
              
            $wave = 1;
            $j--;
        }
    }
}
  
// Driver Code
$arr = array(array(1, 2, 3, 4),
             array(5, 6, 7, 8),
             array(9, 10, 11, 12),
             array(13, 14, 15, 16));                 
WavePrint($R, $C, $arr);
      
// This code is contributed by ajit
?>



Output:

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

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