CC-13 : Matrix shift upwards row wise.

Description:

Given input matrix mat, shift the rows upwards. The first row should rotate to last row.

Test cases and expected outputs:

Input	Expected outputs
mat = { {7,1,4,1}, {9,9,3,0}, {2,1,4,3}, {6,2,7,9}};	9,9,3,0, 2,1,4,3, 6,2,7,9, 7,1,4,1,
mat = { {3,1,2,6,7}, {9,3,2,7,1}, {1,0,0,9,3}, {0,3,6,9,2}, {7,2,4,9,1}};	9,3,2,7,1, 1,0,0,9,3, 0,3,6,9,2, 7,2,4,9,1, 3,1,2,6,7,
mat = { {4,1,7,9,7}, {2,3,6,7,8},};	2,3,6,7,8, 4,1,7,9,7,

Pseudocode:

The java method should accept following input parameters: mat (integer matrix).

Initialize an integer array firstRow with same length as number of columns in mat.

Iterate through mat using a for loop, using variable rIdx as loop counter. Loop variable rIdx will be initialized with value 0 and will iterate through all the matrix’s columns one by one till rIdx < mat.length:

Iterate through mat using a for loop, using variable cIdx as loop counter. Loop variable cIdx will be initialized with value 0 and will iterate through all the matrix’s columns one by one till cIdx < mat[0].length:

If we iterating through the first row, set firstRow[cIdx]=mat[rIdx][cIdx], this will load first row elements into firstRow array.

If we are iterating through the last row, set mat[rIdx][cIdx]=firstRow[cIdx]; this will load first row elements into the last row.

If we are iterating through any other row, set mat[rIdx][cIdx]=mat[rIdx+1][cIdx]; this will shift elements of this row upwards by one row.

After above loops have completed, return mat as the rows have been shifted upwards by one row.

Code:

public int[][] matShiftUpwardRowwise(int[][] mat) throws Exception{
	int[] firstRow=new int[mat[0].length];
	for (int rIdx=0; rIdx < mat.length; rIdx++) {
		for (int cIdx=0; cIdx < mat[0].length; cIdx++) {
			if (rIdx==0) {
				firstRow[cIdx]=mat[rIdx][cIdx];
			}
			if (rIdx==mat.length-1) {
				mat[rIdx][cIdx]=firstRow[cIdx];
			}else {
				mat[rIdx][cIdx]=mat[rIdx+1][cIdx];
			}			
		}
	}
	
	return mat;
}

Click here to download and run code and test cases !

Below fully running code can be copied and run on Eclipse or other Java IDEs. Refer the classname in code below. If the class name below is "A", save the code below to a file named A.java before running it. Be sure to try your own test cases to enhance your understanding ! You can also tweak the code to optimize or add enhancements and custom features.

public class MdArrayShiftUpwardRowwise {
	
public int[][] matShiftUpwardRowwise(int[][] mat) throws Exception{
	int[] firstRow=new int[mat[0].length];
	for (int rIdx=0; rIdx < mat.length; rIdx++) {
		for (int cIdx=0; cIdx < mat[0].length; cIdx++) {
			if (rIdx==0) {
				firstRow[cIdx]=mat[rIdx][cIdx];
			}
			if (rIdx==mat.length-1) {
				mat[rIdx][cIdx]=firstRow[cIdx];
			}else {
				mat[rIdx][cIdx]=mat[rIdx+1][cIdx];
			}			
		}
	}
	
	return mat;
}
	
public static void main(String[] args) {
	MdArrayShiftUpwardRowwise ap=new MdArrayShiftUpwardRowwise();
	int[][] retArr;
	try {
	int[][] arr = {	{7,1,4,1},
					{9,9,3,0},	
					{2,1,4,3},
					{6,2,7,9}
	};
	print2dArray(arr, "The 2d Array");
	retArr=ap.matShiftUpwardRowwise(arr);
	print2dArray(retArr, "Shifted 1 row up");
			
	int[][] arr1 = {	{3,1,2,6,7},
						{9,3,2,7,1},	
						{1,0,0,9,3},
						{0,3,6,9,2},
						{7,2,4,9,1}
								
	};
	print2dArray(arr1, "The 2d Array");
	retArr=ap.matShiftUpwardRowwise(arr1);
	print2dArray(retArr, "Shifted 1 row up");
			
			
	int[][] arr2 = {	{4,1,7,9,7},
						{2,3,6,7,8},	
	};
	print2dArray(arr2, "The 2d Array");
	retArr=ap.matShiftUpwardRowwise(arr2);
	print2dArray(retArr, "Shifted 1 row up");

			
	}catch (Exception exception) {
	System.out.print("Exception,"+ exception);
	exception.printStackTrace();
				
	}
}
			
public static void print2dArray(int[][] intArray, String label) throws Exception {
   	// Case 1: The input Array is null !!
	if (intArray == null) { System.out.println("\n\n Input 2d Array was null !! \n"); return; }
	// Case 2: Print input Array by index (first to last)
	System.out.println();
	System.out.println("*********************************************************************");
	System.out.print(label+" : \n");
	int rIdx=0; int cIdx=0;
	for (rIdx=0; rIdx < intArray.length; rIdx++) {
		for (cIdx=0; cIdx < intArray[rIdx].length; cIdx++) {
			System.out.print(intArray[rIdx][cIdx]);
			if (cIdx < intArray[rIdx].length) System.out.print(",");
		}
		System.out.print("\n");
	} 
	System.out.println();
	System.out.println("**********************************************************************");
	System.out.println();
	Thread.sleep(2000);
	return;	
}					
		
		

}