Need help with arrays (JAVA)

[CreepyPro]

Write a method named collapsePairs that accepts an array of integers as a parameter and modifies the array so that each of its pairs of neighboring integers (such as the pair at indexes 0-1, and the pair at indexes 2-3, etc.) are combined into a single sum of that pair. The sum will be stored at the even index (0,2,4, etc.) if the sum is even and at the odd index (1,3,5, etc.) if the sum is odd. The other index of the pair will change to 0.

 

I can't figure out why I'm not getting the right outpout. For example:

test #1:collapsePairs({7, 2, 8, 9, 4, 22, 7, 1, 9, 10});

 exp. params:{0, 9, 0, 17, 26, 0, 8, 0, 0, 19}

your parameters:{0, 9, 0, 17, 0, 26, 0, 8, 0, 19}

 

 

public static int[] collapsePairs(int[]a) {
		int x[] = new int[a.length];
		for (int i=0; i<a.length-1; i=i+2) {
			if (a[i]+a[i+1]%2==0) 
				x[i]=a[i]+a[i+1];
			else
				x[i+1] = a[i]+a[i+1];
		}
    for(int i=0;i<a.length;i++){
            a[i] = x[i];
    }
	return a;
	}

[BobVonBob]

This is definitely homework so I'll be a bit vague.

 

You're doing something out of order, remember order of operations and think about where it applies in your function.

[TheKDub]

if (a[i]+a[i+1]%2==0) 

 

Double check that line. You're missing something.

[Sauron]

Hey, do you mind marking your other topic as solved before posting another question? Maybe thank the people who helped you while you're at it?

As for this question, there's a mistake in the way you check whether the sum is even or odd. Consider this (check for yourself if you don't believe me):

(4 + 22)%2 = 0 == 0

4 + 22%2 = 4 != 0

[mariushm]

Look at Java Operator Precedence : http://www.cs.bilkent.edu.tr/~guvenir/courses/CS101/op_precedence.html

 

tldr: modulus has higher priority so gets calculated first... and you don't want that. Instruct the compiler to do the addition first by grouping the numbers in something that has higher precendence, like paranthesis for example

So your 

if (a[i]+a[i+1]%2==0) 

can be rewritten as

 

if ( (a[i]+a[i+1]) % 2 == 0) 

 

15

() [] ·

Parentheses Array subscript Member selection

Left to Right

12	* / %	Multiplication Division Modulus	Left to right
11	+ -	Addition Subtraction	Left to right

[Guest]

Look into the
"Binary Search"

[wasab]

Break points and debuggers are your friend. Learn to use them. I also suggest intellij IDE for java.