Pascal's Column Sums

Question

Most everyone here is familiar with Pascal's Triangle. It's formed by successive rows, where each element is the sum of its two upper-left and upper-right neighbors. Here are the first 5 rows (borrowed from Generate Pascal's triangle):

    1
   1 1
  1 2 1
 1 3 3 1
1 4 6 4 1

We're going to take Pascal's Triangle and perform some sums on it (hah-ha). For a given input n, output the columnar sum of the first n rows of Pascal's Triangle. For example, for input 5, the output would be formed by

            1
          1   1
        1   2   1
      1   3   3   1
[+] 1   4   6   4   1
----------------------
    1 1 5 4 9 4 5 1 1

So the output would be [1, 1, 5, 4, 9, 4, 5, 1, 1].

Note that you don't necessarily need to generate Pascal's Triangle to calculate the summation - that's up to your implementation if it's shorter to do so or not.

Input

A single positive integer n with n >= 1 in any convenient format.

Output

The resulting array/list of the column-wise summation of the first n rows of Pascal's triangle, as outlined above. Again, in any suitable format.

Rules

• Leading or trailing newlines or whitespace are all optional, so long as the characters themselves line up correctly.
• Either a full program or a function are acceptable. If a function, you can return the output rather than printing it.
• If possible, please include a link to an online testing environment so other people can try out your code!
• Standard loopholes are forbidden.
• This is code-golf so all usual golfing rules apply, and the shortest code (in bytes) wins.

Examples

[input]
[output]

1
[1]

2
[1, 1, 1]

3
[1, 1, 3, 1, 1]

5
[1, 1, 5, 4, 9, 4, 5, 1, 1]

11
[1, 1, 11, 10, 54, 44, 155, 111, 286, 175, 351, 175, 286, 111, 155, 44, 54, 10, 11, 1, 1]

Answer 1

MATL, 16 bytes

tZv=Gq:"t5BZ+]vs

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Explanation

This repeatedly applies convolution to generate the rows. For example, for input n=5 we start with the first row

0 0 0 0 1 0 0 0 0

Convolving with [1 0 1] gives

0 0 0 1 0 1 0 0 0

Repeating the operation gives

0 0 1 0 2 0 1 0 0

then

0 1 0 3 0 3 0 1 0

etc. Concatenating these arrays vertically and computing the sum of each column gives the result.

t       % Input n implictly. Duplicate
Zv      % Symmetric range. Gives [1 2 3 4 5 4 3 2 1] for input 5
=       % Equal to (element-wise). Gives [0 0 0 0 1 0 0 0 0]. This is the first row
Gq:     % Push [1 2 ... n-1]
"       % For each. This executes the following code n-1 times
  t     %   Duplicate
  5B    %   Push 5 in binary, that is, [1 0 1]
  Z+    %   Convolution keeping size
]       % End
v       % Concatenate all results vertically 
s       % Sum. Display implicitly.

Answer 2

CJam, 32 25 24 bytes

Thanks to Luis Mendo for saving 1 byte.

{(_0a*1+\{_(2$+.+}*]:.+}

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Explanation

(       e# Decrement input N.
_0a*1+  e# Create a list of N-1 zeros and a 1. This is the top row with
        e# the required indentation.
\{      e# Run this block N-1 times.
  _     e#   Duplicate the last row.
  (     e#   Pull off a leading zero, shifting the row left.
  2$+   e#   Copy the full row and prepend that zero, shifting the row right.
  .+    e#   Element-wise addition, which results in the next row.
}*
]       e# Wrap all rows in a list.
:.+     e# Add up the columns by reducing element-wise addition over the rows.

Answer 3

JavaScript (ES6), 90 87 86 84 82 bytes

Saved 3 bytes thanks to ETHproductions

f=(n,a=[1],b=a)=>n--?f(n,[...(F=x=>a.map((n,i)=>n+~~x[i-d]))(a,d=2),0,d=1],F(b)):b

Test cases

f=(n,a=[1],b=a)=>n--?f(n,[...(F=x=>a.map((n,i)=>n+~~x[i-d]))(a,d=2),0,d=1],F(b)):b

console.log(JSON.stringify(f(1)))
console.log(JSON.stringify(f(2)))
console.log(JSON.stringify(f(3)))
console.log(JSON.stringify(f(5)))
console.log(JSON.stringify(f(11)))

Answer 4

Mathematica, 59 57 bytes

Thanks to Martin Ender for finding a two-byte savings!

Binomial[i,(j+i)/2]~Sum~{i,Abs@j,b,2}~Table~{j,-b,b=#-1}&

Pure function taking a positive integer input and returning a list of integers. Literally produces all the relevant entries of Pascal's triangle and sums them appropriately.

Previous submission (which is a bit easier to read):

Table[Sum[Binomial[i,(j+i)/2],{i,Abs@j,b,2}],{j,-b,b=#-1}]&

Answer 5

JavaScript (ES6), 83 bytes

f=
n=>[...Array(n+--n)].map(g=(j=n,i,a)=>j--?g(j,i-1)+g(j,i+1)+(a?g(j,i,a):0):i-n?0:1)

<input type=number min=1 oninput=o.textContent=f(+this.value)><pre id=o>

1-indexing cost me a byte. Explanation: g(j-1,i-1)+g(j-1,i+1) recursively calculates Pascal's triangle until it reaches the first row, which is the base case. To obtain column sums, I use the fact that map actually passes a third parameter, so there is an extra recursive step when this is the case.

Answer 6

05AB1E, 34 32 28 25 24 bytes

-4 thanks to Emigna.

FN©ƒ®Ne0})¹®-Å0.ø˜¨ˆ}¯øO

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---

FN©ƒ®Ne0})               # Generate, iteratively, the current pascal row, interspersed with 0's.
          ¹®-Å0          # Calculate the number of zeros to middle pad it.
               .ø˜¨ˆ}¯øO # Surround with the zeros, transpose and sum.

---

Basically all it does is generate this:

0 0 0 0 0 0 1 0 0 0 0 0 0
0 0 0 0 0 1 0 1 0 0 0 0 0
0 0 0 0 1 0 2 0 1 0 0 0 0
0 0 0 1 0 3 0 3 0 1 0 0 0
0 0 1 0 4 0 6 0 4 0 1 0 0

Transpose it:

0 0 0 0 0
0 0 0 0 1
0 0 0 1 0
0 0 1 0 4
0 1 0 3 0
1 0 2 0 6
0 1 0 3 0
0 0 1 0 4
0 0 0 1 0
0 0 0 0 1
0 0 0 0 0

Then sums each row:

0
1
1
5
4
9
4
5
1
1
0

---

If a leading and trailing 0 are not acceptable, ®>-Å isntead of ®-Å fixes it for a +1 byte penalty.

---

Result for 50:

[0, 1, 1, 50, 49, 1224, 1175, 19551, 18376, 229125, 210749, 2100384, 1889635, 15679951, 13790316, 97994765, 84204449, 523088334, 438883885, 2421229251, 1982345366, 9833394285, 7851048919, 35371393434, 27520344515, 113548602181, 86028257666, 327340174085, 241311916419, 851817398634, 610505482215, 2009517658701, 1399012176486, 4313184213360, 2914172036874, 8448367214664, 5534195177790, 15139356846901, 9605161669111, 24871748205410, 15266586536299, 37524050574849, 22257464038550, 52060859526501, 29803395487951, 66492351226050, 36688955738099, 78239857877649, 41550902139550, 84859704298201, 43308802158651, 84859704298201, 41550902139550, 78239857877649, 36688955738099, 66492351226050, 29803395487951, 52060859526501, 22257464038550, 37524050574849, 15266586536299, 24871748205410, 9605161669111, 15139356846901, 5534195177790, 8448367214664, 2914172036874, 4313184213360, 1399012176486, 2009517658701, 610505482215, 851817398634, 241311916419, 327340174085, 86028257666, 113548602181, 27520344515, 35371393434, 7851048919, 9833394285, 1982345366, 2421229251, 438883885, 523088334, 84204449, 97994765, 13790316, 15679951, 1889635, 2100384, 210749, 229125, 18376, 19551, 1175, 1224, 49, 50, 1, 1, 0]

Answer 7

Octave, 84 67 45 bytes

22 bytes saved thanks to Neil!

@(n)sum(spdiags(flip(tril(flip(pascal(n))))))

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Explanation

The pascal function gives a matrix that contains the values in the Pascal triangle:

>> pascal(5)
ans =
     1     1     1     1     1
     1     2     3     4     5
     1     3     6    10    15
     1     4    10    20    35
     1     5    15    35    70

To extract the desired values we flip vertically (flip), keep the lower triangular part (tril ), and flip again. This gives

ans =
   1   1   1   1   1
   1   2   3   4   0
   1   3   6   0   0
   1   4   0   0   0
   1   0   0   0   0

spdiags then extracts the diagonals as columns

ans =
   1   1   1   1   1   0   0   0   0
   0   0   4   3   2   1   0   0   0
   0   0   0   0   6   3   1   0   0
   0   0   0   0   0   0   4   1   0
   0   0   0   0   0   0   0   0   1

and sum computes the sum of each column, which gives the result.

Answer 8

PHP, 119 bytes

columns numbers from 1-input to input -1

for(;$r<$argn;$l=$t[+$r++])for($c=-$r;$c<=$r;$c+=2)$s[$c]+=$t[+$r][$c]=$r|$c?$l[$c+1]+$l[$c-1]:1;ksort($s);print_r($s);

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Answer 9

Jelly, 12 bytes

Ḷµc€j€0Ṛṙ"NS

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How it works

Ḷµc€j€0Ṛṙ"NS  Main link. Argument: k

Ḷ             Unlength; yield A := [0, ..., k-1].
 µ            New chain. Argument: A
  c€          Combinations each; compute nCr for each n and r in A, grouping by n.
    j€0       Join each resulting array [nC0, ..., nC(k-1)], separating by zeroes,
              yielding, [nC0, 0, ..., 0, nC(k-1)].
              Note that nCr = 0 whenever r > n.
       Ṛ      Reverse the resulting 2D array.
          N   Negate A, yielding [0, ..., -(k-1)].
        ṙ"    Zipwith rotate; for each array in the result to the left and the
              corresponding integer non-positive integer to the right, rotate
              the array that many units to the left.
           S  Take the columnwise sum.

Answer 10

Python 3, 201 184 bytes

def f(n):x,z,m=[1],[0],n-1;l=[z*m+x+z*m];exec("x=[*map(sum,zip(z+x,x+z))];l.append(z*(n-len(x))+[b for a in zip(x,z*len(x))for b in a][:-1]+z*(n-len(x)));"*m);return[*map(sum,zip(*l))]

Answer 11

Haskell, 118 112 104 bytes

6 14 bytes saved thanks to @nimi

z=zipWith(+)
p n|n<2=[1]|m<-p(n-1)=z(0:0:m)(m++[0,0])            -- Generate the nth triangle row.
f n=foldl1 z[d++p x++d|x<-[1..n],d<-[0<$[1..n-x]]]  -- Pad each row with 0s and then sum all the rows.

Answer 12

Python 2, 140 137 bytes

n=input()
x=[]
a=[0]*n+[1]+n*[0]
z=n%2
exec'x+=[a];a=[(i%2^z)*sum(a[i-1:i+2])for i in range(2*n+1)];z^=1;'*n
print map(sum,zip(*x))[1:-1]

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^{For n=3}
Starts with a list with n zeros surround an one - [[0, 0, 0, 1, 0, 0, 0]]
Generate the full pyramid

[[0, 0, 0, 1, 0, 0, 0],
 [0, 0, 1, 0, 1, 0, 0],
 [0, 1, 0, 2, 0, 1, 0]]

Rotate 90º and sum each row, discarding the first and the last one (only zeros)

[[0, 0, 0],
 [0, 0, 1],
 [0, 1, 0],
 [1, 0, 2],
 [0, 1, 0],
 [0, 0, 1],
 [0, 0, 0]]

Answer 13

Python 3, 124 chars

f=lambda n:[sum(map(lambda n,k:k<1or (2*k+n)*f(2*k+n-1,k-1)/k,[abs(x)]*n,range(n))[:(n+1-abs(x))/2]) for x in range(-n+1,n)]

This uses the fact that the Pascal Triangle can be defined with binomial coefficents. I tried removing the abs(x) and the range(-n+1,n) by making it range(n) and then using lambda l:l[-1:0:-1]+l but it was longer.

Also this is my first time golfing so I hope you forgive any faux-pas.

The binomial is not mine and was taken from here.