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Solve Generate Target Expressions using Lua Language

Solve Generate Target Expressions using Lua to enhance your skills with lua coding practice , master coding concepts, and prepare for interviews with practical exercises and detailed solutions.

Generate Target Expressions

Difficulty : Hard

Categories :

  • Recursion

Given two integers n and k, output an array of all possible expressions that evaluate to n using exactly k numbers from 1 to 9, using only addition (+) and multiplication (*) operators. Each number can be used at most once.

Each expression should:

  • Contain exactly k digits from 1-9
  • Use only + and * operators (no subtraction or division)
  • Not have leading zeros
  • Follow standard operator precedence (* before +)
  • Return expressions in lexicographical order

Constraints:

  • 1 ≤ n ≤ 10^4
  • 1 ≤ k ≤ 9
  • Must use recursion in the solution

Examples:

Input: n = 11, k = 2
Output: ["2+9", "3+8", "4+7", "5+6"]
Explanation: All possible expressions using 2 digits that equal 11
Input: n = 24, k = 3
Output: ["1*3*8", "1*4*6", "1+4*5", "1*8+16", "2*3*4", "2+2*11", "3*1*8", "3+3*7"]
Explanation: All expressions evaluate to 24 using 3 digits

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Choose from the following categories

Strings A sequence of characters used to represent text, with problems focused on manipulation, searching, and pattern matching.

Arrays A collection of elements stored in contiguous memory locations, allowing efficient random access and manipulation.

Linked Lists A linear data structure where each element (node) points to the next, offering dynamic memory allocation and efficient insertions/deletions.

Trees A hierarchical data structure with nodes connected by edges, used in applications like databases, file systems, and parsing.

Graphs A collection of nodes (vertices) connected by edges, representing relationships, widely used in networking, routing, and social networks.

Dynamic Programming An optimization technique that solves problems by breaking them into overlapping subproblems and storing their results.

Backtracking A problem-solving method that explores all possibilities recursively, backtracking when a solution is not feasible.

Sorting Algorithms Techniques for arranging elements in a specific order, such as quicksort, mergesort, and bubble sort, essential for data organization.

Searching Algorithms Methods for finding elements in a dataset, such as binary search, linear search, and graph traversal techniques.

Mathematics A field of study involving numbers, calculations, and logical reasoning, forming the foundation for algorithms and problem-solving.

Recursion A programming technique where a function calls itself to solve smaller instances of the same problem, often used in divide-and-conquer approaches.

Bit Manipulation Operations performed directly on binary representations of data, used for efficient computations and optimization tasks.