Program to reverse the rows in a 2d Array
Given a 2D array arr[][] of size M x N integers where M is the number of rows and N is the number of columns. The task is to reverse every row of the given 2D array.
Example:
Input: arr[][] =
{ {1, 2, 3},
{4, 5, 6},
{7, 8, 9} }
Output:
3 2 1
6 5 4
9 8 7
Input: arr[][] =
{ {1, 2},
{4, 5},
{7, 8},
{9, 10} }
Output:
2 1
5 4
8 7
10 9
Approach:
- For every row in the given 2D array do the following:
- Intialise the start index as 0 and end index as N-1.
- Iterate loop till start index is less than ending index, swap the value at these indexes and update the index as:
swap(arr[i][start], arr[i][end]) start++; end--;
- Do the above operation for all the rows in the 2D array.
Below is the implementation of the above approach:
C++
// C++ implementation of the above approach#include <bits/stdc++.h>using namespace std;const int M = 3;const int N = 3;// A utility function// to swap the two elementvoid swap(int* a, int* b){ int temp = *a; *a = *b; *b = temp;}// Function to reverse// the given 2D arr[][]void reverseArray(int arr[M][N]){ // Traverse each row of arr[][] for (int i = 0; i < M; i++) { // Initialise start and end index int start = 0; int end = N - 1; // Till start < end, swap the element // at start and end index while (start < end) { // Swap the element swap(&arr[i][start], &arr[i][end]); // Increment start and decrement // end for next pair of swapping start++; end--; } } // Print the arr[][] after // reversing every row for (int i = 0; i < M; i++) { for (int j = 0; j < N; j++) { cout << arr[i][j] << ' '; } cout << endl; }}// Driver Codeint main(){ int arr[][3] = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } }; // Function call reverseArray(arr); return 0;} |
Java
// Java implementation of the above approachclass GFG{ static int M = 3;static int N = 3; // Function to reverse// the given 2D arr[][]static void reverseArray(int arr[][]){ // Traverse each row of arr[][] for (int i = 0; i < M; i++) { // Initialise start and end index int start = 0; int end = N - 1; // Till start < end, swap the element // at start and end index while (start < end) { // Swap the element int temp = arr[i][start]; arr[i][start] = arr[i][end]; arr[i][end] = temp; // Increment start and decrement // end for next pair of swapping start++; end--; } } // Print the arr[][] after // reversing every row for (int i = 0; i < M; i++) { for (int j = 0; j < N; j++) { System.out.print(arr[i][j] + " "); } System.out.println(); }} // Driver Codepublic static void main(String[] args){ int arr[][] = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } }; // Function call reverseArray(arr);}}// This code is contributed by PrinciRaj1992 |
Python3
# Python3 implementation of the above approachM = 3;N = 3;# Function to reverse# the given 2D arr[][]def reverseArray(arr) : # Traverse each row of arr[][] for i in range(M) : # Initialise start and end index start = 0; end = N - 1; # Till start < end, swap the element # at start and end index while (start < end) : # Swap the element arr[i][start], arr[i][end] = arr[i][end], arr[i][start]; # Increment start and decrement # end for next pair of swapping start += 1; end -= 1; # Print the arr[][] after # reversing every row for i in range(M) : for j in range(N) : print(arr[i][j],end= ' '); print(); # Driver Codeif __name__ == "__main__" : arr = [ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ]; # Function call reverseArray(arr); # This code is contributed by AnkitRai01 |
C#
// C# implementation of the above approachusing System;class GFG{ static int M = 3;static int N = 3; // Function to reverse// the given 2D [,]arrstatic void reverseArray(int [,]arr){ // Traverse each row of [,]arr for (int i = 0; i < M; i++) { // Initialise start and end index int start = 0; int end = N - 1; // Till start < end, swap the element // at start and end index while (start < end) { // Swap the element int temp = arr[i,start]; arr[i, start] = arr[i, end]; arr[i, end] = temp; // Increment start and decrement // end for next pair of swapping start++; end--; } } // Print the [,]arr after // reversing every row for (int i = 0; i < M; i++) { for (int j = 0; j < N; j++) { Console.Write(arr[i, j] + " "); } Console.WriteLine(); }} // Driver Codepublic static void Main(String[] args){ int [,]arr = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } }; // Function call reverseArray(arr);}}// This code is contributed by PrinciRaj1992 |
Javascript
<script>// JavaScript implementation of the above approach const M = 3; const N = 3; // Function to reverse // the given 2D arr function reverseArray(arr) { // Traverse each row of arr for (i = 0; i < M; i++) { // Initialise start and end index var start = 0; var end = N - 1; // Till start < end, swap the element // at start and end index while (start < end) { // Swap the element var temp = arr[i][start]; arr[i][start] = arr[i][end]; arr[i][end] = temp; // Increment start and decrement // end for next pair of swapping start++; end--; } } // Print the arr after // reversing every row for (i = 0; i < M; i++) { for (j = 0; j < N; j++) { document.write(arr[i][j] + " "); } document.write("<br/>"); } } // Driver Code var arr = [ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ]; // Function call reverseArray(arr);// This code is contributed by todaysgaurav</script> |
Output:
3 2 1 6 5 4 9 8 7
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