Check If It Is a Good Array

class Solution:
    def isGoodArray(self, nums: List[int]) -> bool:
        def gcd(a, b):
            while b:
                a, b = b, a % b
            return a

        g = nums[0]
        for num in nums:
            g = gcd(g, num)

        return g == 1

This solution checks whether there exists a subset of numbers whose greatest common divisor (GCD) is 1, which will make the array good. It calculates the GCD of all elements in the array using the helper function gcd(). If the GCD is 1, then there exists a subset that can be used to obtain a sum of 1.

10 Prerequisite LeetCode Problems

“1250. Check If It Is a Good Array” requires an understanding of number theory, specifically concepts like Bezout’s Identity and the greatest common divisor (GCD). Here are some related problems:

  1. “365. Water and Jug Problem”: This problem also uses Bezout’s Identity, which is crucial for “Check If It Is a Good Array”.
  2. “204. Count Primes”: An introduction to number theory.
  3. “231. Power of Two”: A problem dealing with number properties.
  4. “326. Power of Three”: Similar to above, another number property problem.
  5. “762. Prime Number of Set Bits in Binary Representation”: A more complex number theory problem.
  6. “868. Binary Gap”: This problem involves number manipulation and understanding of binary numbers.
  7. “412. Fizz Buzz”: Simple manipulation and checking of numbers.
  8. “263. Ugly Number”: This problem introduces the concept of factorization.
  9. “202. Happy Number”: This problem involves manipulating numbers in a unique way and checking for specific conditions.
  10. “1071. Greatest Common Divisor of Strings”: This problem gives practice with GCD in a different context, working with strings instead of numbers.

Problem Classification

This is an array subset selection problem that involves evaluating multiplicative combinations. It falls under the domain of combinatorics and number theory.

The key ‘What’ components are:

  • An array of positive integers
  • Selecting a subset of the array elements
  • Multiplying the subset elements by arbitrary integers
  • Checking if a sum of 1 can be obtained
  • Determining if such a subset and multiplicands exist

Based on these aspects, we can categorize this problem as:

  • Combinatorics - Selecting and evaluating subsets
  • Number theory - Properties of multiplication and addition
  • Array manipulation - Selecting array elements
  • Validation - Checking if desired combination exists

So in summary, this is a validation problem focused on determining if a subset-multiplicand combination exists that produces a desired numerical result. It involves combinatorial generation and evaluation along with number theory constraints. The core challenge is efficiently searching the space of possibilities.

Distilling the Problem to Its Core Elements

  1. This problem is based on the fundamental concepts of combinatorics and modular arithmetic. It involves generating and evaluating subsets under multiplicative transformations.

  2. I would describe this problem simply as: “Given a set of numbers, can you pick some, multiply them by other numbers, and get a sum of 1?”

  3. The core problem is determining if a subset-multiplicand combination exists that produces 1. We can simplify it to: “Does a combination exist that sums to 1?”

  4. The key components are:

  • The input array of integers
  • Generating subset combinations
  • Trying different multiplicands
  • Evaluating the sum
  • Checking if 1 is achievable
  1. The minimum operations are:
  • Enumerate subsets
  • Try multiplicand options
  • Compute sum of multiplied elements
  • Check if sum equals 1
  • Return true if match found, false otherwise

This problem focuses on searching through the space of subsets and multiplicands and checking if 1 is achievable, rather than actually finding the optimal combination.

Visual Model of the Problem

Here are some ways we could visualize this problem statement:

  • Show the input array visually as a sequence of numbered boxes

  • Use a tree diagram to illustrate the possible subsets that can be generated from the input array

  • Animate the process of selecting a subset, multiplying the elements, and computing the sum

  • Use a flow chart to demonstrate the key steps - generate subsets, multiply elements, compute sum, check for 1, return true/false

  • Provide examples of arrays with visuals showing a subset & multiplicands that evaluate to 1

  • Similarly show counter examples of arrays where 1 cannot be obtained

  • Use bar charts to compare valid vs invalid combinations and sums

  • Leverage visual libraries like D3.js to create interactive range sliders for exploring multiplicands

  • Animate the array, allowing interactivity to select subsets and multiplicands and see the resulting sum

The goal is to visually demonstrate the process of generating combinations and evaluating them against the target value. Both valid and invalid examples help build intuition about the constraints. Interactivity also aids understanding.

Problem Restatement

Here’s how I would paraphrase the problem statement in my own words:

We are given an array of positive integers. Our goal is to determine if we can select a subset of the array elements, multiply each of them by some integer values, and obtain a sum of 1.

Specifically, we need to check if there exists some combination of:

  • Picking a subset of numbers from the input array
  • Multiplying each selected number by an arbitrary integer (can be negative)
  • Summing up the resulting multiplied numbers

That gives us an end result of 1.

The key aspects are:

  • The multiplicands can be any integer, positive or negative
  • We only care about existence - finding one combination that works
  • The order of elements does not matter
  • No constraints on the size of subset or multiplicand values

In summary, we need to determine if some selection and multiplication of the input array elements can be combined in a way that sums to 1. The focus is on finding one valid combination rather than the actual elements or multiplicands themselves.

Does this help summarize the essence of the problem? Let me know if any part needs more clarification or I’m missing anything important.

Abstract Representation of the Problem

Here is one way to formulate an abstract representation of this problem:

Let’s define:

  • S = The set of all possible subsets of the input array

  • M = The set of all possible integer multiplicand values

  • f = A function that takes a subset s ∈ S and set of multiplicands m ∈ M and computes the sum of multiplied elements

Then the problem reduces to:


  • Set S of all subsets
  • Set M of all multiplicands
  • Summation function f


  • If any s ∈ S and m ∈ M exist such that f(s, m) = 1


  • True if such an s and m exist where f(s, m) = 1
  • False otherwise

In essence, we have a universe of subsets and multiplicative scaling factors, and want to determine if any combination of them produces the target value when evaluated under the summation function.

The problem is distilled into its core elements - a space of states, transformations, and checking a predicate over state combinations. Let me know if you would modify or clarify this abstraction in any way!


Here are some key terms and concepts relevant to this problem:

Combinatorics - Field focused on counting combinations and permutations of sets. Needed to generate subsets.

Modular arithmetic - Math operations performed on integers modulo some number. Required to check sum vs target.

Subset - A set containing some elements of a larger set. We need to generate and evaluate subsets.

Multiplicands - The integers that array elements are multiplied by. Must try different values.

Commutativity - Order of elements does not affect result. Allows flexibility in solutions.

Brute force - Trying all possibilities through exhaustive search. A straightforward but inefficient approach.

Pruning - Eliminating branches unlikely to lead to valid solutions. Useful for optimization.

Heuristics - Functions guiding search direction based on problem insights. Can help prune and direct.

Key concepts include leveraging combinatorics to generate subsets, modular arithmetic to evaluate combinations, and optimizations like pruning and heuristics to efficiently search the solution space. The terms help shape approaches for both modeling and implementation.

Problem Simplification and Explanation

Here’s one way I can explain this problem in simpler terms:

Key Concepts:

  • Array - The input is an array of integer numbers

  • Subset - We need to select a subset of the array numbers

  • Multiplication - Each number in the subset is multiplied by some integer

  • Summation - The multiplied numbers are summed up

  • Target - The goal is to obtain a target sum value (1)


Imagine the array is a basket of numbered apples. We want to pick some apples from the basket, scale their numbers up or down by multiplying, then add the results.

The question is - by picking some apples and scaling their numbers arbitrarily, can we end up with a sum of 1?

It’s like changing the prices on some items in your shopping cart and asking if there is some way they could add up to exactly $1. We don’t care which items specifically or how much you change them by - just that some combination exists.

In essence, we search for a subset-multiplicand combination that produces the desired sum. The core is efficiently exploring the combinations rather than actual construction.


Here are some characteristics of the problem that we can potentially leverage for an efficient solution:

  • Array contains only positive integers - This bounds the search space and transformations needed to hit 1. Negative multiplicands are enough without fractions or decimals.

  • No constraints on subset size - We can pick as many or few elements as needed. This provides more options to hit the target sum.

  • Multiplicands can be any integer - This allows both scaling up and down as needed. Both directions help expand options.

  • Commutativity of multiplication/addition - Order doesn’t matter, allowing more flexible solutions.

  • Output is binary, not actual subset/multiplicands - We can stop as soon as any valid combination is found rather than finding all possible ones.

  • No constraints on efficiency - Simpler brute force approaches may be acceptable depending on input size.

  • Upper bound on array size - 10^5 allows certain brute force solutions that wouldn’t scale beyond a point.

These properties give us a lot of flexibility by allowing unconstrained transformations in both directions. We can likely get away with simpler exhaustive searches rather than complex optimizations early on. The limited input domain also bounds the search space.

Here are some key insights gained by analyzing the constraints:

  • Positive integer array bounds the transformations needed to hit the target sum. We only need negative multiplicands rather than fractions or decimals.

  • No limits on subset size gives flexibility in combinations to try. We can use as many or few elements as needed.

  • Unconstrained multiplicands allow both scaling up and down as required. Two-way transformations expand possibilities.

  • Commutative property lets us disregard order and rearrange elements freely.

  • Binary output means we can stop at the first valid find rather than finding all combinations.

  • No efficiency constraints allow even brute force approaches depending on input size.

  • Capped maximum size enables brute force solutions that won’t work at larger scales.

Overall, these constraints mean we can likely use simple exhaustive search approaches as opposed to complex optimizations early on. The limited domain and flexibility minimizes the need for pruning the search space.

We can focus first on correct subset generation and transformation logic rather than efficiency. The insights help scope the solution space.

Case Analysis

Here are some additional test cases covering different aspects:

  1. Simple valid case

Input: [2, 4, 5] Output: True

Analysis: Basic case with small valid input.

  1. Larger values

Input: [123, 734, 211] Output: True

Analysis: Handles larger input values.

  1. No multiplicand

Input: [1, 1, 1] Output: True

Analysis: Multiplicand of 1 allows hitting target.

  1. Negative multiplicands

Input: [2, 3, 4] Output: True

Analysis: Checks use of negative multiplicands.

  1. No solution

Input: [2, 3] Output: False

Analysis: Validates unachievable target handled.

Edge cases:

  • Single element array
  • Repetitive values
  • Extremely large values
  • Max array size

The key aspects tested are multiplicands, input values, and solvability. Edge cases cover degenerate inputs.

Here are some key insights gained from analyzing these test cases:

  • Simple valid cases with small inputs are useful for initial validation of core logic. They serve as a minimal baseline.

  • Testing larger input values reveals assumptions about constraints on value ranges.

  • Multiplicand edge cases like 1 or negative numbers validate flexibility in transformations.

  • Unsolvable inputs ensure the solution properly identifies when target cannot be reached.

  • Single element and repetitive value arrays verify logic handles degenerate edge cases.

  • Extreme values stress test numeric limits and overflow assumptions.

  • Maximum size array checks scale robustness and constraints.

  • A wide range aimed at covering the input space builds confidence in correctness.

  • Input parameters like value spread and array size help generate insights around complexity.

Overall, these cases validate the core transformation and evaluation logic across the input range, include degenerate situations, and test scale assumptions - highlighting both functional and performance considerations.

Identification of Applicable Theoretical Concepts

Here are some mathematical and algorithmic concepts that could help solve this problem:

  • Combinatorics - Subset generation, permutation algorithms to create options to evaluate

  • Dynamic programming - Store intermediate subset sums to avoid recomputing

  • Pruning strategies - Eliminate branches unlikely to lead to 1 based on bounds

  • Heuristics - Prioritize selections/multiplicands based on magnitude or properties

  • Modular arithmetic - Perform sum calculations modulo target for efficiency

  • Bitmasking - Compactly represent subset options as bit vectors for fast generation

  • Mathematical optimization - Formulate as integer program with subset as variables

  • Parallel processing - Evaluate multiple combinations concurrently to accelerate

  • Memoization - Cache results for duplicate subproblems to avoid redundancy

Concepts from combinatorics, algorithms, optimization, and number theory provide useful techniques for generating options, evaluating them intelligently, and improving efficiency. We can balance simplicity and performance based on constraints.

Problem Breakdown and Solution Methodology

Here is a step-by-step explanation of how I would approach solving this problem:

  1. Generate all possible subsets of the input array
  • The powerset contains all options we need to evaluate
  1. Try all possible multiplicand values for each subset
  • Attempt both positive and negative integers as scaling factors
  1. Multiply each subset element by the chosen multiplicand

  2. Sum the resulting multiplied values

  3. Check if the sum equals 1

  • If so, return true, we found a valid combination

  • If not, try the next multiplicand option

  1. If all options exhausted, return false

This brute force approach systematically checks all combinations by generating all subsets, trying all multiplicands, evaluating the sum, and checking against the target.

Visualizing the tree of possibilities helps illustrate the exhaustive exploration. Pruning branches with bounds on sum could optimize it.


Input: [2, 5, 7]

Try subset [2, 5]

Attempt multiplicands -1, 1, 2, etc.

Check -22 + 51 = 1, return true

The key is incrementally trying all combinations and short circuiting when target found.

Inference of Problem-Solving Approach from the Problem Statement

How did you infer from the problem statement that this problem can be solved using ?

Stepwise Refinement

Here is one way to break this problem down into more granular steps:

High-level approach:

  1. Generate all possible subsets
  2. Check if any combine to reach target sum

Refined steps:

  1. Write subset generation logic
  • Initialize powerset as [[]]
  • Iterate over array, adding element to each subset
  1. Define evaluation function:
  • Take subset and multiplicand values
  • Multiply elements and compute sum
  • Check if sum is target
  1. Try all multiplicand options:
  • Attempt both positive and negative integers
  • Break if target sum reached
  1. Check each subset:
  • Pass to evaluation function
  • Break and return true if sum reached
  1. If all subsets checked, return false

Independent parts:

  • Subset generation
  • Combination evaluation
  • Checking target reached

Repeatable patterns:

  • Iterating over array to build combinations
  • Trying different transformation options
  • Evaluating against target sum

This breaks down subset generation, combinatorial evaluation, and result checking into modular steps. The evaluation logic can be reused across subsets.

Solution Approach and Analysis

Here is a step-by-step explanation of how I would approach solving this problem:

  1. Generate all subsets of the input array
  • Start with empty set and incrementally add elements using bitmasks, recursion etc.
  1. Define a function to evaluate a subset and multiplicands
  • Take a subset and array of multiplicands as input
  • Multiply each subset element and compute sum
  • Check if sum equals target value
  1. Loop through each subset
  • Try all possible multiplicand values, both positive and negative
  • Pass subset and multiplicands to evaluation function
  • If true returned, end loop and return true
  1. If all subsets checked, return false

This generates all subset options upfront using combinatorics techniques, then evaluates each by trying different multiplicative transformations.

As an example on [2, 4]:

  1. Powerset is [[], [2], [4], [2,4]]

  2. Try multiplicands -1, 1 for [2]: 2*(-1) = -2, not 1

  3. Try multiplicands for [4]: 4*(1) = 4, not 1

  4. Try multiplicands for [2,4]: 2*(-1) + 4*(1) = 1, return true

The key is separating out subset generation from evaluation logic, and trying all combinations exhaustively. Caching could optimize repeated work.

Thought Process

Claude generates buggy code. SKIPPING.

From Brute Force to Optimal Solution

Could you please begin by illustrating a brute force solution for this problem? After detailing and discussing the inefficiencies of the brute force approach, could you then guide us through the process of optimizing this solution? Please explain each step towards optimization, discussing the reasoning behind each decision made, and how it improves upon the previous solution. Also, could you show how these optimizations impact the time and space complexity of our solution?

Code Explanation and Design Decisions

  1. Identify the initial parameters and explain their significance in the context of the problem statement or the solution domain.

  2. Discuss the primary loop or iteration over the input data. What does each iteration represent in terms of the problem you’re trying to solve? How does the iteration advance or contribute to the solution?

  3. If there are conditions or branches within the loop, what do these conditions signify? Explain the logical reasoning behind the branching in the context of the problem’s constraints or requirements.

  4. If there are updates or modifications to parameters within the loop, clarify why these changes are necessary. How do these modifications reflect changes in the state of the solution or the constraints of the problem?

  5. Describe any invariant that’s maintained throughout the code, and explain how it helps meet the problem’s constraints or objectives.

  6. Discuss the significance of the final output in relation to the problem statement or solution domain. What does it represent and how does it satisfy the problem’s requirements?

Remember, the focus here is not to explain what the code does on a syntactic level, but to communicate the intent and rationale behind the code in the context of the problem being solved.

Coding Constructs

Consider the following piece of complex software code.

  1. What are the high-level problem-solving strategies or techniques being used by this code?

  2. If you had to explain the purpose of this code to a non-programmer, what would you say?

  3. Can you identify the logical elements or constructs used in this code, independent of any programming language?

  4. Could you describe the algorithmic approach used by this code in plain English?

  5. What are the key steps or operations this code is performing on the input data, and why?

  6. Can you identify the algorithmic patterns or strategies used by this code, irrespective of the specific programming language syntax?

Language Agnostic Coding Drills

Your mission is to deconstruct this code into the smallest possible learning units, each corresponding to a separate coding concept. Consider these concepts as unique coding drills that can be individually implemented and later assembled into the final solution.

  1. Dissect the code and identify each distinct concept it contains. Remember, this process should be language-agnostic and generally applicable to most modern programming languages.

  2. Once you’ve identified these coding concepts or drills, list them out in order of increasing difficulty. Provide a brief description of each concept and why it is classified at its particular difficulty level.

  3. Next, describe the problem-solving approach that would lead from the problem statement to the final solution. Think about how each of these coding drills contributes to the overall solution. Elucidate the step-by-step process involved in using these drills to solve the problem. Please refrain from writing any actual code; we’re focusing on understanding the process and strategy.

Targeted Drills in Python

Now that you’ve identified and ordered the coding concepts from a complex software code in the previous exercise, let’s focus on creating Python-based coding drills for each of those concepts.

  1. Begin by writing a separate piece of Python code that encapsulates each identified concept. These individual drills should illustrate how to implement each concept in Python. Please ensure that these are suitable even for those with a basic understanding of Python.

  2. In addition to the general concepts, identify and write coding drills for any problem-specific concepts that might be needed to create a solution. Describe why these drills are essential for our problem.

  3. Once all drills have been coded, describe how these pieces can be integrated together in the right order to solve the initial problem. Each drill should contribute to building up to the final solution.

Remember, the goal is to not only to write these drills but also to ensure that they can be cohesively assembled into one comprehensive solution.


Similar Problems

Can you suggest 10 problems from LeetCode that require similar problem-solving strategies or use similar underlying concepts as the problem we’ve just solved? These problems can be from any domain or topic, but they should involve similar steps or techniques in the solution process. Also, please briefly explain why you consider each of these problems to be related to our original problem.