CC-17 : Generate Pascal’s Triangle.

Description:

Pascal’s triangle consists of rows of integers formatted to be displayed as a triangle. In rows of the triangle, the first and last elements are always 1. The other elements in rows (other than first and last) are sum of elements directly above it in previous row. Given input integer reqRows, generate and return a Pascals triangle with that may rows multidimensional int array.

Test cases and expected outputs:

Input	Expected outputs
reqRows=3	1 1 1 1 2 1
reqRows=4	1 1 1 1 2 1 1 3 3 1
reqRows=5	1 1 1 1 2 1 1 3 3 1 1 4 6 4 1

Pseudocode:

The java method should accept following input parameters: int reqRows.

Declare a multidimensional array pTriangle with reqRows rows and undeclared columns.

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:

Declare pTriangle[rIdx] row to be an int array with rIdx+1 rows.

o 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 cIdx is first or last column of current row, set current element to 1 using pTriangle[rIdx][cIdx]=1.

Else set current element to sum of numbers above it using pTriangle[rIdx][cIdx]=pTriangle[rIdx-1][cIdx]+pTriangle[rIdx-1][cIdx-1].

Print the value of pTriangle[rIdx][cIdx].

After above loops are completed, pTriangle contains the generated Pascals triangle with required number of rows. Return pTriangle.

Code:

public int[][] matPascalTriangle(int reqdRows) throws Exception{
	int[][] pTri = new int [reqdRows][];
	for (int rIdx=0; rIdx < reqdRows; rIdx++) {
		pTri[rIdx]=new int[rIdx+1];
		System.out.print("\n");
		for (int cIdx=0; cIdx < pTri[rIdx].length; cIdx++){
			if ((rIdx-1 <0)|| (cIdx-1<0) || (cIdx>=pTri[rIdx-1].length)) {
				pTri[rIdx][cIdx]=1;					
			}else {
				pTri[rIdx][cIdx]=pTri[rIdx-1][cIdx]+pTri[rIdx-1][cIdx-1];
			}
			System.out.print(pTri[rIdx][cIdx]);
			System.out.print("  ");
		}
	}
	return pTri;		
}

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 MdArrayPascalTriangle {
	

public int[][] matPascalTriangle(int reqdRows) throws Exception{
	int[][] pTri = new int [reqdRows][];
	for (int rIdx=0; rIdx < reqdRows; rIdx++) {
		pTri[rIdx]=new int[rIdx+1];
		System.out.print("\n");
		for (int cIdx=0; cIdx < pTri[rIdx].length; cIdx++){
			if ((rIdx-1 <0)|| (cIdx-1<0) || (cIdx>=pTri[rIdx-1].length)) {
				pTri[rIdx][cIdx]=1;					
			}else {
				pTri[rIdx][cIdx]=pTri[rIdx-1][cIdx]+pTri[rIdx-1][cIdx-1];
			}
			System.out.print(pTri[rIdx][cIdx]);
			System.out.print("  ");
		}
	}
	return pTri;		
}
	
	
    
public static void main(String[] args) {
	MdArrayPascalTriangle ap= new MdArrayPascalTriangle();
	try {
			
	ap.matPascalTriangle(3);
	ap.matPascalTriangle(4);
	ap.matPascalTriangle(5);
		
		
	}catch (Exception exception) {
	System.out.print("Exception: "+ exception);
	}
				
}

}