CodeReportSolutions

Code Report Solutions

Following are some simple solutions to videos found on YouTube. Idea is to make it easier for comparing and learning z^3 and other beautiful languages.

Number of Different Integers in a String

Video: https://www.youtube.com/watch?v=59vAjBS3yZM [APL Wins (vs C++, Java & Python)]

z^3 Solution

s="ad3343sadfsd343434df343443sff";
(s#/[^\d]+/)∪

Result: 3343	343434	343443


 # splits string using the postfix regexp pattern. ∪ extracts unique from the results
 12 Character z^3 Solution vs. 14 Character APL Solution
 
 

Another Solution

 s="ad3343sadfsd343434df343443sff";
(/\d+/g!)(s)#;

Answer: 3. Uses RegExp, and ! is used to create a predicate function to match the RegExp. String is given to the predicate function, and # counts the number of pieces extracted.

Final Value of Variable After Performing Operations

Video: https://www.youtube.com/watch?v=8Njxgy4itts [4 APL Solutions in 10 Minutes!]

z^3 Solution

m=["--x","x++","x++"].print();
[0]@(m!)

Gives answer:

x	[--x,x++,x++]
0	-1	-1	0

m! makes this to a function which is evaluated using [0]@. 0 forms a single input combinatorial argument.
[0..10]@(m!) can be used to loop through a set of initial values

Interesting that this solution has far less characters than APL solution, and  can be made even shorter.

Count Negative Numbers in a Sorted Matrix

Video: https://www.youtube.com/watch?v=pDbDtGn1PXk [LeetCode 176 Problem 1 - Count Negative Numbers in a Sorted Matrix]

z^3 Solution

x=[-2,-1,0;-1,1,3;-1,2,4];
(x⍌).findv(NEGATIVE)#

Gives answer 4

⍌ Flatten Array
.findv Gives result of function call NEGATIVE 
# Counts the result
Also note simpler z^3 Array Notation used to create the variable x (with , and ;). Usual Javascript array notations also work.

Check if a matrix is an X-Matrix (X like diagonals are filled)

Video: https://www.youtube.com/watch?v=8ynsN4nJxzU [APL vs BQN vs J vs Q vs NumPy vs Julia vs R - A comparison of seven different programming languages across a few different language criteria.]

z^3 Solution

m=[2 0 0 1; 0 3 1 0; 0 5 2 0; 4 0 0 2];
n=(m#)[0];
xm=|n| |+| |n|.reverse();
xm|==|(m.$("x!=0?1:0"!))

Gives answer true

m# gives length of array m. 
|n| gives n dimensional Identity Matrix, which is added using |+| to the .reverse() of same array.
|==| is used to compare this to the m, .$ is used to apply the function "x!=0?1:0"! to every element. "x!=0?1:0"! shows how a function can be created from a string with the ! operator.
Also note simpler z^3 Array Notation used to create the variable x (with , (when positive numbers alone are used, the comma is also optional) and ;). Usual Javascript array notations also work.

Sign of Product of an Array

Video: https://www.youtube.com/watch?v=a7CSK7HNEWQ&t=297s [I ❤ APL and Haskell #2 ]

z^3 Solution

a=[-1,-2,-3,4,3,2,1];
∏±a

Gives answer -1

∏ is Product, ± is SIGN function. APL has 3 characters it its solution (selected as the best solution in the video because of its brevity). Interesting that the solution with z^3 has even less characters, just 2.

Powerful Solution to Indexing Problem (1 character in z^3 vs 3 in APL)

Video: https://www.youtube.com/watch?v=ctbGMuakpHk [Python vs 3 Character APL Solution ]

z^3 Solution

a=[0,2,1,5,3,4];
a#a

Gives answer 0 1 2 4 5 3

Actual logic is just # [Hash], which is an index access operator, if operated on any array. For this problem, the answer is just one character (3 to be generous). # operator is far more powerful and is polymorphic depending on the types of arguments it operators on.

Partitioning Odd and Even Numbers in an Array

Video: https://www.youtube.com/watch?v=A16w7qTfT68 [Implementing C++'s std::partition in BQN ]

z^3 Solution

a=[3,1,2,4];
(a ⑂ [ISEVEN,ISODD]) ⍌

Gives answer 2 4 3 1

Fork (⑂) with an array of functions, and flatten the result. Function Array can have any number of predicates/functions.

Rearrange Array to Maximize Prefix Score

Video: https://www.youtube.com/watch?v=mRT-yK2RTdg [Why I Love BQN So Much! (vs Python)]

z^3 Solution

a=[2,-1,0,1,-3,3,-3];
((a⋱) ≡⧺ ∑)  ↥;

Gives answer 6

Sort by Descending Order (⋱), followed by cumulative row SUM (≡⧺ SUM), followed by MAX (↥)

Hypotenuse

Video: https://www.youtube.com/watch?v=Wah-uQ9ou80 [Python vs Uiua vs BQN]

z^3 Solution

h:=√∑([a,b]^2);
h(3,4)

Gives answer 5

Filter Is Odd From List

Video: https://www.youtube.com/watch?v=XJ3QWOSZ8Nk [Lightning Talk: C++ vs Haskell vs BQN by Conor Hoekstra | Lambda Days 2023]

z^3 Solution

(1..5) ⑂ ISODD

Gives answer 1 3 5

Greatest Common Divisor/Lowest Common Multiple

Video: https://www.youtube.com/watch?v=UVUjnzpQKUo [1 Problem, 16 Programming Languages (C++ vs Rust vs Haskell vs Python vs APL...)]

z^3 Solution

LCM(20,15)
Gives: 60
GCD(20,15)
Gives: 5
GCD(5..20..5,15)
Gives:
-	GCD
5	15	5
10	15	5
15	15	15
20	15	5

Maximum Count of Positive Integer and Negative Integer

Video: https://www.youtube.com/watch?v=U6I-Kwj-AvY&list=PLVFrD1dmDdvf8REa4SkI-IppFGvkRq83O [1 Problem, 24 Programming Languages]

z^3 Solution

Examples:
a=[-2,-1,-1,1,2,3];
b=[-3,-2,-1,0,0,1,2];
c=[5,20,66,1314];


a=[-2,-1,-1,1,2,3];
b=[-3,-2,-1,0,0,1,2];
c=[5,20,66,1314];

[
 (a ⑂) ≡ ⧻,
 (b ⑂) ≡ ⧻,
 (c ⑂) ≡ ⧻
]

Answer:
3 0 3
3 2 2
0 0 4


 ⑂ - SPLIT INTO NEGATIVE,ZERO,POSITIVE (by default, or any array of boolean functions)
 ≡ - BYROW
 ⧻ - COUNT

Richest Customer Wealth

Video: https://www.youtube.com/watch?v=MKb4WD6mioE [1 Problem, 6 Programming Languages (C++ vs Rust vs Haskell vs APL vs Clojure vs Scala)]

z^3 Solution

w=[
	[1,2,3],
	[5,5,5],
	[3,1,4]	
];
(w≡∑)↥
Answer:
15

 ≡ - BYROW
 ∑ - SUM
 ↥ - MAX

Extract First 4 Words

Video: https://www.youtube.com/watch?v=a7CSK7HNEWQ [I ❤ APL and Haskell]

z^3 Solution

s="This is a sentence which has a lot of words";
(s#" ")#(0..3)
 
 s="Hello how are you Contestant";
(s#" ")#(0..3)
Answer:
This	is	a	sentence
Hello	how	are	you

 #" " Splits the sentence by words
 #(0..3) Extracts first four elements (or) words.
 
 

PowerSet Sum of Powers

Video: https://www.youtube.com/watch?v=k9BNn39gWiM [BQN vs Jelly]

Powers of the Powerset. Power is defined as the square of the largest number in a sequence, multiplied by the smallest.

z^3 Solution

p=POWERSET([2,1,4]);
p≡"[∏(↧x,↥x^2)]"!.*∑;
 
Answer:
141

 "[∏(↧x,↥x^2)]"!  Creates a function (with the fabulous operator !) of product of min and square of max. ! makes a function out of a string.
 ≡ Apply the function by row
 .*∑ applies ∑ to the array on the left 
 
 

Left and Right Sum Differences

Video: https://www.youtube.com/watch?v=i1K_kUKJnE4 [I ❤ BQN and Haskell]

Problem Link: https://leetcode.com/contest/weekly-contest-334/problems/left-and-right-sum-differences/

Given a 0-indexed array nums, find a 0-indexed integer array answer where:

answer.length==nums.length.

answer[i]=|leftSum[i]-rightSum[i]|

Where:

-leftSum[i] is the sum of elements to the left of the index i in the array nums. If there is no such element, leftSum[i]=0

-rightSum[i] is the sum of elements to the right of the index i in the array nums. If there is no such element, rightSum[i]=0

z^3 Solution

xs=[10,4,8,3];
n=(xs#1d)[0];
a=[0]⧺ (xs#(0..(n-2))) ≡⧺(SUM);
b=[0]⧺(xs#((n-1)..(1)..-1)) ≡⧺(SUM); 
b⤽;
(a|-|b).$(ABS);

Answer:
15	1	11	22

≡⧺ Cumulate an array with function (SUM).
 ⧺  Concat
 ⤽  Reverse
 |-| Element wise Subtraction
 #1d Size of 1st Dimension with [0] to index the number.
 
 

Sum of Squares of Elements with Index that are Factors of the Length of the Array

Video: https://www.youtube.com/watch?v=SpZJxbOf_jM&list=PLVFrD1dmDdvd_rChH0L1jeMVZpJ8ZIivE [BQN vs Uiua #2]

z^3 Solution

a=[1,2,3,4];
b=[2,7,1,19,18,3];
x=a;
n=x⧻;
m=NOT(n|%|(1..n));
∑((x◍m)²);


Answer:
With x=a: 21

With x=b: 63

 ⧻  Length
 |%|  Array Mod
 |-| Element wise Subtraction
 mask Extract Elements that Match Mask Array (with Null if second parameter is TRUE).
 n|%|(1..n) gets indices that are factors of the length n
 ◍  .mask 
 ²  SQUARED, POWERED TO 2
 ∑  SUM