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squareUp  challenge

Posted on 2016-08-14
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Hi,

I am working on below challenge
http://codingbat.com/prob/p155405

Array-3 > squareUp
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Given n>=0, create an array length n*n with the following pattern, shown here for n=3 : {0, 0, 1,    0, 2, 1,    3, 2, 1} (spaces added to show the 3 groups).

squareUp(3) → [0, 0, 1, 0, 2, 1, 3, 2, 1]
squareUp(2) → [0, 1, 2, 1]
squareUp(4) → [0, 0, 0, 1, 0, 0, 2, 1, 0, 3, 2, 1, 4, 3, 2, 1]
0
Question by:gudii9
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• +1

LVL 7

Author Comment

ID: 41756424
Given n>=0, create an array length n*n with the following pattern, shown here for n=3 : {0, 0, 1,    0, 2, 1,    3, 2, 1} (spaces added to show the 3 groups).

squareUp(3) → [0, 0, 1, 0, 2, 1, 3, 2, 1]
squareUp(2) → [0, 1, 2, 1]
squareUp(4) → [0, 0, 0, 1, 0, 0, 2, 1, 0, 3, 2, 1, 4, 3, 2, 1]

i have not understood the challenge description.

How below are expected outputs?

squareUp(3) → [0, 0, 1, 0, 2, 1, 3, 2, 1]
squareUp(2) → [0, 1, 2, 1]
squareUp(4) → [0, 0, 0, 1, 0, 0, 2, 1, 0, 3, 2, 1, 4, 3, 2, 1]
0

LVL 38

Accepted Solution

Gerwin Jansen, EE MVE earned 1000 total points
ID: 41756439
You shift the numbers into the array from the right in groups. Example for 5:

0,0,0,0,1
0,0,0,2,1
0,0,3,2,1
0,4,3,2,1
5,4,3,2,1
0

LVL 27

Expert Comment

ID: 41756501
As a warm-up, how would you make an array that contained the integers from  0  to  n² -1 ??
0

LVL 7

Author Comment

ID: 41756527
You shift the numbers into the array from the right in groups. Example for 5:

0,0,0,0,1
0,0,0,2,1
0,0,3,2,1
0,4,3,2,1
5,4,3,2,1
this is clear now. let me think on it now
0

LVL 38

Expert Comment

ID: 41756564
OK ;)
0

LVL 7

Author Comment

ID: 41760204
looks like i may need two loops for this also
0

LVL 7

Author Comment

ID: 41760209
You shift the numbers into the array from the right in groups. Example for 5:
how to represent this push in code?
0

LVL 27

Assisted Solution

d-glitch earned 500 total points
ID: 41760380
You shift the numbers into the array from the right in groups. Example for 5:
0,0,0,0,1
0,0,0,2,1
0,0,3,2,1
0,4,3,2,1
5,4,3,2,1

You don't have to build the array by shifting.

What numbers are in the first row?
And the second?
Do you see the pattern?
And the pattern in the number of 0's?
0

LVL 7

Author Comment

ID: 41764758
not yet
0

LVL 36

Assisted Solution

mccarl earned 500 total points
ID: 41764796
not yet

Wow, how about now with some extra spaces in certain spots...

0,0,0,0,     1
0,0,0,     2,1
0,0,     3,2,1
0,     4,3,2,1
5,4,3,2,1
0

LVL 27

Expert Comment

ID: 41765353
"Wow" indeed.
Do you realize that printing the array in an n x n grid rather than an n² x 1 string is an enormous hint?
0

LVL 7

Author Comment

ID: 41765452
Do you realize that printing the array in an n x n grid rather than an n² x 1 is an enormous hint?
not able to realize. I just see some additional spaces.

0,0,0,0,1
0,0,0,2,1
0,0,3,2,1
0,4,3,2,1
5,4,3,2,1

compared to above below?

0,0,0,0,     1
0,0,0,     2,1
0,0,     3,2,1
0,     4,3,2,1
5,4,3,2,1
0

LVL 27

Expert Comment

ID: 41765550
There are two ways to build an array with n² elements:

for i= 0 to n² by 1

for i= 0 to n by 1
for j= 0 to n by 1

The second method might be useful if you can see the pattern in the grid.
0

LVL 7

Author Comment

ID: 41767259
for i= 0 to n by 1
for j= 0 to n by 1

The second method might be useful if you can see the pattern in the grid.

which grid? what is grid?
you mean below?
0,0,0,0,     1
0,0,0,     2,1
0,0,     3,2,1
0,     4,3,2,1
5,4,3,2,1

to me above looks lik e2 D array not 1 Dimensional?
0

LVL 27

Expert Comment

ID: 41767319
Yes, you have to build a 1-D array.
Gerwin Jansen gave you an enormous hint by drawing it as an nxn matrix so you can see the pattern.
1

LVL 38

Expert Comment

ID: 41767330
The grid is the 2D array we've shown you to help understand the question. Your function should return a single string of numbers.

squareUp(2) → [0, 1, 2, 1]
0,1
2,1

squareUp(1) → [0, 1]
0
1
0

LVL 27

Expert Comment

ID: 41767502
I am sure this is not correct.  There can only be n*n elements.
squareUp(1) → [0, 1]

0
1

The answer is probably [1], but it may depend on your implementation.

And squareUp(0) → [ ]  because it must have 0*0 elements.
0

LVL 38

Expert Comment

ID: 41767626
@d-glitch - You are correct, 1*1=1 :D

squareUp(1) would have to result in [1] - independent of the implementation.

Each group is n wide starting with a 1 on the right side, this would result in [1]
0

LVL 7

Author Comment

ID: 41767634
``````public int[] squareUp(int n) {

int[] finalRes = new int[n * n];
int indx = 0;

for (int i = 1; i <= n; i++) {
for (int k = 1; k <= n - i; k++)
finalRes[indx++] = 0;
for (int j = i; j > 0; j--)
finalRes[indx++] = j;
}
return finalRes;

}
``````

above passes all tests.
Expected      Run
squareUp(3) → [0, 0, 1, 0, 2, 1, 3, 2, 1]      [0, 0, 1, 0, 2, 1, 3, 2, 1]      OK
squareUp(2) → [0, 1, 2, 1]      [0, 1, 2, 1]      OK
squareUp(4) → [0, 0, 0, 1, 0, 0, 2, 1, 0, 3, 2, 1, 4, 3, 2, 1]      [0, 0, 0, 1, 0, 0, 2, 1, 0, 3, 2, 1, 4, 3, 2, 1]      OK
squareUp(1) → [1]      [1]      OK
squareUp(0) → []      []      OK
squareUp(6) → [0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 2, 1, 0, 0, 0, 3, 2, 1, 0, 0, 4, 3, 2, 1, 0, 5, 4, 3, 2, 1, 6, 5, 4, 3, 2, 1]      [0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 2, 1, 0, 0, 0, 3, 2, 1, 0, 0, 4, 3, 2, 1, 0, 5, 4, 3, 2, 1, 6, 5, 4, 3, 2, 1]      OK

All Correct

any improvements/refinements/alternate approaches?
0

LVL 38

Expert Comment

ID: 41767645
It is passing all tests, code looks OK to me.
0

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