CC-19 :Reshape matrix as per input rows and columns.

Description:

Given input int matrix mat, reshape it into a new matrix as per required rows and columns.

Test cases and expected outputs:

Input	Expected outputs
reqRows=1, reqCols=9 mat = { {0,1,2}, {3,4,5}, {6,7,8}};	Reshaped Matrix 1x9: 0,1,2,3,4,5,6,7,8,
reqRows=2, reqCols=4 mat = { {1,2}, {3,4}, {5,6}, {7,8}};	Reshaped Matrix 2x4: 1,2,3,4, 5,6,7,8,
reqRows=6, reqCols=2 mat = { {1,2,3,4}, {5,6,7,8}, {9,10,11,12}};	Reshaped Matrix 6x2: 1,2, 3,4, 5,6, 7,8, 9,10, 11,12,

Pseudocode:

The java method should accept following input parameters: mat (int square matrix), int reqRows, int reqCols.

If number of elements in mat not equal to reqRows*reqCols; then return null as the input matrix cannot be reshaped as per requirements.

Declare an int matrix nMatrix of size reqRows * reqCols to hold the reshaped matrix.

Initialize 2 int variables newrIdx=0 and newcIdx=0; these variable will hold indexes of new reshaped matrix.

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:

Set nMatrix[newrIdx][newcIdx]= mat[rIdx][cIdx].

Increment newcIdx by 1.

Check if (newcIdx>= reqCols) if so we need to move to next row of nMatrix:

newcIdx=0;

newrIdx++;

After above loops are completed, mat has been reshaped to nMatrix with required rows and columns. Return nMatrix.

Code:

public int[][] matReshape(int[][] mat, int reqRows, int reqCols) throws Exception{
	if ((mat.length*mat[0].length) != (reqRows*reqCols)) { return null;}
	int[][] nMatrix=new int[reqRows][reqCols];
	int newrIdx=0; int newcIdx=0;
	for (int rIdx=0; rIdx < mat.length; rIdx++) {
		for (int cIdx=0; cIdx< mat[0].length; cIdx++) {
			nMatrix[newrIdx][newcIdx]= mat[rIdx][cIdx];
			newcIdx++;
			if (newcIdx>= reqCols) {
				newcIdx=0; 
				newrIdx++;				
			}
		}
	}	
	return nMatrix;
}

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 MdArrayReshape {
	
public int[][] matReshape(int[][] mat, int reqRows, int reqCols) throws Exception{
	if ((mat.length*mat[0].length) != (reqRows*reqCols)) { return null;}
	int[][] nMatrix=new int[reqRows][reqCols];
	int newrIdx=0; int newcIdx=0;
	for (int rIdx=0; rIdx < mat.length; rIdx++) {
		for (int cIdx=0; cIdx< mat[0].length; cIdx++) {
			nMatrix[newrIdx][newcIdx]= mat[rIdx][cIdx];
			newcIdx++;
			if (newcIdx>= reqCols) {
				newcIdx=0; 
				newrIdx++;				
			}
		}
	}	
	return nMatrix;
}
	
public static void main(String[] args) {
	MdArrayReshape ap=new MdArrayReshape();
	int[][] retArr;
	try {
	int[][] arr = {	{0,1,2},
					{3,4,5},	
					{6,7,8}
	};
	print2dArray(arr, "The 2d Array");
	retArr=ap.matReshape(arr,1,9);
	print2dArray(retArr, "Reshaped Matrix 1x9");
	
	int[][] arr1 = {	{1,2,3,4},
						{5,6,7,8},	
						{9,10,11,12}};
	print2dArray(arr1, "The 2d Array");
	retArr=ap.matReshape(arr1,6,2);
	print2dArray(retArr, "Reshaped Matrix 6x2");
	
			
	int[][] arr2 = 	{	{1,2},
						{3,4},	
						{5,6},
						{7,8}								
	};
	print2dArray(arr2, "The 2d Array");
	retArr=ap.matReshape(arr2,2,4);
	print2dArray(retArr, "Reshaped Matrix 2x4");
			
	}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;	
}				
		
		

}