Java Program to Modify a matrix by rotating ith row exactly i times in clockwise direction

Given a matrix mat[][] of dimensions M * N, the task is to print the matrix obtained after rotating every i^th row of the matrix i times in a clockwise direction.

Examples:

Input: mat[][] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}
Output:
1 2 3
6 4 5
8 9 7
Explanation:
The 0^th row is rotated 0 times. Therefore, the 0^th row remains the same as {1, 2, 3}.
The 1^st row is rotated 1 times. Therefore, the 1^st row modifies to {6, 4, 5}.
The 2^nd row is rotated 2 times. Therefore, the 2^nd row modifies to {8, 9, 7}.
After completing the above operations, the given matrix modifies to {{1, 2, 3}, {6, 4, 5}, {8, 9, 7}}.

Input: mat[][] = {{1, 2, 3, 4}, {4, 5, 6, 7}, {7, 8, 9, 8}, {7, 8, 9, 8}}
Output:
1 2 3 4
7 4 5 6
9 8 7 8
8 9 8 7

Approach: Follow the steps below to solve the problem:

• Traverse the given matrix in row – wise manner and for every i^th row, perform the following steps:
  • Reverse the current row of the matrix.
  • Reverse the first i elements of the current row.
  • Reverse the last (N – i) elements of the current row, where N is the current size of the row.
• After completing the above steps, print the matrix mat[][].

Below is the implementation of the above approach:

Java

// java program for the above approach
import java.io.*;
import java.lang.*;
import java.util.*;

class GFG {

  // Function to reverse arr[] from start to end
  static void reverse(int arr[], int start, int end)
  {
    while (start < end) {
      int temp = arr[start];
      arr[start] = arr[end];
      arr[end] = temp;
      start++;
      end--;
    }
  }

  // Function to rotate every i-th
  // row of the matrix i times
  static void rotateMatrix(int mat[][])
  {
    int i = 0;

    // Traverse the matrix row-wise
    for (int rows[] : mat) {

      // Reverse the current row
      reverse(rows, 0, rows.length - 1);

      // Reverse the first i elements
      reverse(rows, 0, i - 1);

      // Reverse the last (N - i) elements
      reverse(rows, i, rows.length - 1);

      // Increment count
      i++;
    }

    // Print final matrix
    for (int rows[] : mat) {
      for (int cols : rows) {
        System.out.print(cols + " ");
      }
      System.out.println();
    }
  }

  // Driver Code
  public static void main(String[] args)
  {

    int mat[][] = { { 1, 2, 3 },
                   { 4, 5, 6 },
                   { 7, 8, 9 } };

    rotateMatrix(mat);
  }
}

// This code is contributed by Kingash.

Output:

1 2 3 
6 4 5 
8 9 7

Time Complexity: O(N*M), as we are using nested loops to traverse N*M times.

Auxiliary Space: O(1), as we are not using any extra space.

Please refer complete article on Modify a matrix by rotating ith row exactly i times in clockwise direction for more details!