CC-8 : Count negative elements in a matrix.

Description:

Given input matrix mat, where each row of matrix is individually sorted incrementally, we need to traverse it and count the elements that are negative.

Test cases and expected outputs:

Input	Expected outputs
mat = { {-2,-1,5,6}, {0,3,5,7}, {-4,-3,-2,-1}}	Matrix has 6 negative numbers.
mat= { {-4,1,5,6}, {-6,-3,0,16}, {-9,-6,-3,0} }	Matrix has 6 negative numbers.

Pseudocode:

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

Initialize a variable nCnt to hold the count of negative numbers found 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 mat[rIdx][cIdx] is negative, increment nCnt by 1.

If mat[rIdx][cIdx] is 0 or positive, exit the inner loop. This is because the rows are sorted, so once we find 0 or positive number, then we will not find any further negative numbers in that row.

• Once above loops are completed, return nCnt.

Code:

public int matArrayCountNegatives(int[][] mat) throws Exception{
	int nCnt=0; 
	for (int rIdx=0; rIdx < mat.length; rIdx++) {
		for (int cIdx=0; cIdx < mat[0].length; cIdx++) {
			if (mat[rIdx][cIdx] < 0 ) {
				nCnt++;
			}else {
				break;
			}
		}		
	}	
	return nCnt;
}

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 MdArrayCountNegatives {
	
public int matArrayCountNegatives(int[][] mat) throws Exception{
	int nCnt=0; 
	for (int rIdx=0; rIdx < mat.length; rIdx++) {
		for (int cIdx=0; cIdx < mat[0].length; cIdx++) {
			if (mat[rIdx][cIdx] < 0 ) {
				nCnt++;
			}else {
				break;
			}
		}		
	}	
	return nCnt;
}
	
public static void main(String[] args) {
	MdArrayCountNegatives ap=new MdArrayCountNegatives();
	int nCnt;
	try {
	int[][] arr = {	{-2,-1,5,6},
					{0,3,5,7},	
					{-4,-3,-2,-1}
	};
	print2dArray(arr, "The 2d Array");
	nCnt=ap.matArrayCountNegatives(arr);
	System.out.println("Matrix has "+nCnt+ " negative numbers.");
			
	int[][] arr1 = {	{-4,1,5,6},
						{-6,-3,0,16},	
						{-9,-6,-3,0}
	};
	print2dArray(arr1, "The 2d Array");
	nCnt=ap.matArrayCountNegatives(arr1);
	System.out.println("Matrix has "+nCnt+ " negative numbers.");
			
			
	}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;	
}					
		
		

}