Javascript: matrix, how to get sum of that numbers which are not 0

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I have a F(x) function which gets matrix`
F([
[0,1,5,2],
[1,0,2,0],
[0,0,3,4]
]);
I need make 0 that numbers which above number also 0. As a result i must get this`
[
[0,1,5,2],
[0,0,2,0],
[0,0,3,0]
];
Then i need count sum of that numbers which are not 0. As a result i must get this`
13(1+5+2+2+3=13).

What I have tried:

I have tried like this but it returns 11.

function F(x){
	var sum = 0;
	for(var i = 0; i < x.length; i++){
		for(var j = i; j < x.length; j++){
			if(x[i][j] == 0){
				x[i+1][j] = 0;
			}
			if(x[i][j] != 0){
				sum += x[i][j];
			}
		}
	}
	return sum;
}
console.log(F([[0,1,5,2],[1,0,2,0],[0,0,3,4]]));

Posted 26-Jul-18 22:28pm

Suren97

Updated 26-Jul-18 23:26pm

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2 solutions

Solution 1

JavaScript

for(var j = i; j < x.length; j++){

The value for j should be going from 0 to 3 (4 columns) but your code has it going from i (which may be 0, 1 or 2) to 2. So you will be ignoring some columns in the matrix.

Posted 26-Jul-18 22:36pm

Richard MacCutchan

Comments

Suren97 27-Jul-18 4:38am

this way it gives error` Cannot set property '0' of undefined

Richard MacCutchan 27-Jul-18 4:46am

What way?

Suren97 27-Jul-18 4:49am

for(var j = 0; j < 4; j++)

Richard MacCutchan 27-Jul-18 5:19am

If i has the value 2, it is on the last row, so i+1 is an undefined reference.

Suren97 27-Jul-18 5:21am

so what should i write bro?

Richard MacCutchan 27-Jul-18 5:22am

Check whether you are on the last line. Try thinking about the logic of your program before you start coding, so you know exactly what steps to take and in what order.

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*dan!sh* · Accepted Answer · 2018-07-26T23:27:00

There are few problems here. One is the starting index for j. It should be 0. Second, the code in the loop itself. For every item, you should be checking item above it and not the one below. Once i = length, i + 1 will result in error. Also, the limit value in second for loop may or may not be same as first one. You basically have an array of arrays. A bit more general solutions could be something like this:

JavaScript

function F(x){
	var sum = 0;
	for(var i = 0; i < x.length; i++){
		for(var j = 0; j < x[i].length; j++){
			// Check for previous element
                        if(i>0){
                            if(x[i-1][j] > 0){
                            sum += x[i][j];
                            }
                        }
            else{
            sum += x[i][j];
            }
		}
	}
	
    return sum;
   
}

This still assumes that all sub-arrays have same number of elements. If there are differences in them too, you will need to check for length of previous array.