5 Best Ways to Check if Array Sum Can Be Made K Using Three Operations in Python

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πŸ’‘ Problem Formulation: We are looking to determine whether we can manipulate the sum of the elements in an array to equal a specified target value (k) by applying at most three operations: adding, subtracting, or replacing elements. Given an array like [1, 2, 3] and a target sum, say k = 6, we aim to establish the possibility of reaching this sum using three operations.

Method 1: Brute Force Iteration

The Brute Force Iteration approach exhaustively checks all possible combinations of additions, subtractions, and replacements that could be performed on the array’s elements to achieve the target sum k. This method leverages nested loops and conditionals to explore each possible operation on the items.

Here’s an example:

def can_make_sum_k(arr, k):
    n = len(arr)
    for i in range(n):
        for change in (-arr[i], arr[i]):
            other_sum = sum(arr) - arr[i] + change
            if other_sum == k:
                return True
    return False

# Example usage
print(can_make_sum_k([1, 2, 3], 6))

Output: True

The function can_make_sum_k iterates through each element in the array and tests whether replacing it with its negative or keeping it the same, then summarizing the array results in the target sum k. It returns True as soon as it finds one such combination.

Method 2: Using Set for Look-up

Exploiting a set for potential sums can significantly reduce the time complexity. This method entails creating a set of all possible sums after three operations, and then checking if k is present within this set.

Here’s an example:

def can_make_sum_k_set(arr, k):
    potential_sums = {sum(arr)}
    for x in arr:
        # Add combinations with +x and -x
        potential_sums.update({current_sum + x for current_sum in potential_sums})
        potential_sums.update({current_sum - x for current_sum in potential_sums})
    return k in potential_sums

# Example usage
print(can_make_sum_k_set([1, 2, 3], 6))

Output: True

The can_make_sum_k_set function cleverly builds a set of potential sums after applying either of the operations to each number in the original array. It then simply checks if the desired sum k is within this set. It’s a more efficient approach, especially when dealing with larger arrays.

Method 3: Dynamic Programming

Dynamic Programming can be applied as an optimization to avoid the redundant calculation of the same subproblems. This approach stores intermediate results to be reused, which can be essential when working with larger arrays where redundancies are more common.

Here’s an example:

def can_make_sum_k_dp(arr, k):
    sum_arr = sum(arr)
    dp = {0}
    for num in arr:
        temp = set()
        for sum_ in dp:
            temp.add(sum_ + num)
            temp.add(sum_ - num)
            temp.add(sum_)
        dp = temp
    return k in dp

# Example usage
print(can_make_sum_k_dp([1, 2, 3], 6))

Output: True

The function can_make_sum_k_dp creates a dynamic programming (DP) set to store all unique sums achievable at each step, incorporating each new element with addition, subtraction, or no operation. If the target sum k is in DP, we know we can achieve it.

Method 4: Recursive Backtracking

Recursive Backtracking is a depth-first search approach that explores each possibility of achieving the target sum k. Backtracking allows undoing operations if they lead to a dead end, enabling a systematic search for a valid solution.

Here’s an example:

def can_make_sum_k_recur(arr, k, index=0, current_sum=0):
    if index == len(arr):
        return current_sum == k
    # Choose to add, subtract, or skip the current element
    return (can_make_sum_k_recur(arr, k, index + 1, current_sum + arr[index]) or
            can_make_sum_k_recur(arr, k, index + 1, current_sum - arr[index]) or
            can_make_sum_k_recur(arr, k, index + 1, current_sum))

# Example usage
print(can_make_sum_k_recur([1, 2, 3], 6))

Output: True

The function can_make_sum_k_recur recurses through the array, at each step either adding, subtracting, or not using the current element to build towards the target sum k. If any of the recursive paths return True, the function concludes that the target sum is achievable.

Bonus One-Liner Method 5: Pythonic Intuition with itertools

With Python’s itertools module, one can generate combinations of operations in a Pythonic manner. This method harnesses combinations of operators in a single line, offering a clever and concise way to address the problem.

Here’s an example:

from itertools import product

def can_make_sum_k_pythonic(arr, k):
    return any(sum(x) == k for x in product(*[(num, -num, 0) for num in arr]))

# Example usage
print(can_make_sum_k_pythonic([1, 2, 3], 6))

Output: True

The can_make_sum_k_pythonic function uses the itertools.product function to create a generator for all possible sum combinations of the original array with its negative and zero elements, then checks if any sum equals k. It is extremely concise but can be less efficient because it considers all operation combinations.

Summary/Discussion

  • Method 1: Brute Force Iteration: Simple to understand. Best for small arrays. Poor efficiency for large arrays.
  • Method 2: Using Set for Look-up: Improves performance by avoiding redundancy. Less understandable than brute force. More efficient as array size increases.
  • Method 3: Dynamic Programming: Optimizes recurring computations. Complex to implement. Highly efficient for large arrays with repeated sums.
  • Method 4: Recursive Backtracking: Systematical approach to finding a solution. May be slower due to recursive overhead. Efficient with pruning techniques.
  • Bonus Method 5: Pythonic Intuition with itertools: Extremely concise. Pythonic in nature. Not efficient for large arrays due to exhaustive combination generation.