Questions tagged [recursive-backtracking]

Recursive backtracking is a general algorithm for finding solutions to computational problems that incrementally builds partial solutions and drops those which are identified as futile *as early as possible*.

Recursive backtracking is a general algorithm for finding solutions to computational problems that incrementally builds partial solutions and drops as early as possible those partial solutions which are identified as futile i.e. such that can not lead to a correct solution.

It essentially involves building nested loops through recursion. Each loop embodies a series of choices. Each inner loop can accept a partial-solution-so-far and try its own choices in a loop, or reject the partial solution it is presented with, through early exit or an equivalent of the continue or break etc. statement.

The control is inverted in that the full solution is achieved in the innermost loop, which can act on it in a particular manner, like printing it to the output / external file, or calling a callback with the solution as an argument.

The backtracking computational structure is embodied in the states of the nested loops, in each of the nested loops' loop variables.

314 questions
1
vote
2 answers

Algorithm to generate all nonnegative solutions to x1 + x2 + ....xk = n. (Stars and bars)

What is an algorithm to generate every solution to x1 + x2 + ....xk = n, xi >= 0? I am aware it is some form of backtracking but I am not sure how to implement this.
1
vote
1 answer

list value remains changed after returning from the backtracking function

class Solution: def generateParenthesis(self, n: int) -> List[str]: ans = [] def backtrack(S, left, right): if len(S) == 2 * n: ans.append(''.join(S)) return if left < n: …
R__
  • 87
  • 5
1
vote
0 answers

Power Set in Lexicographic order. Recursion and bactracking

I am new to recursion and backtracking. How the code after the recursive call is being executed? class Solution { // str : Stores input string // n : Length of str. // curr : Stores current permutation // index : Index in current permutation,…
1
vote
1 answer

Why do we need to copy array element inside backtracking

This is a classic backtracking problem , i dont know why we need to copy arr element inside recursive function in order for it to work correctly. If i dont copy. It will return blank array def subsets(self, nums: List[int]) -> List[List[int]]: …
1
vote
1 answer

Why is my code giving time-limit exceeded while a near identical code works just fine in LeetCode?

Ref: https://leetcode.com/problems/word-search/submissions/ Brief problem statement: Given a matrix of characters and a string, does the string exist in this matrix. Please refer the above link for details. Solution-1 Gives time-limit…
1
vote
0 answers

Backtracking algorithm - trying to find a better solution

I’d like to ask for a little bit of help with a project I’m currently working on, where I’m supposed to create a sort of “organizing program” using backtracking. The story is, I have a given number of animals, each with their own type, habitat, and…
Matt
  • 21
  • 3
1
vote
1 answer

How to print path during backtracking?

I am currently working on a backtracking program and was asked to print the path for the result. Here's an example: Imagine we are given a weighted graph, represented by adjacency list, g, g = { "A": {"B": 6, "D": 1}, "B": {"A": 6, "C": 5,…
1
vote
1 answer

Recursive solution to counting the number of ways you can go up a staircase

I'm trying to solve the problem of "count ways to reach the nth step in a staircase" with recursion. When given a number of stairs to climb, I have to calculate the number of ways to climb taking either 1 or 2 steps at a time. For example, if there…
1
vote
1 answer

Create a list of combinations recursively

I am trying to implement a combination method using recursion. I have already done it using a for loop but want to approach it via recursion. The method gets two inputs and creates all possible combinations. It is supposed to store the combination…
user14153071
1
vote
0 answers

What is the difference between passing by reference and passing by value of arrays for recursive calls which share a reference via a closure?

I was working on a solution to the following prompt: Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order. The following code passes the tests: /** * @param {number[]} nums *…
1
vote
1 answer

Recursive Backtracking Does Not Back Track

I have been struggling to solve the following question using Recessive Backtracking in C++. The problem is that it does not backtrack. I tracked my algorithm manually on a paper and it works on the paper. So problem is I don't know how to implement…
Max
  • 509
  • 1
  • 7
  • 21
1
vote
1 answer

TLE in Word Search backtracking

Here is a problem from Leetcode: Given an m x n grid of characters board and a string word, return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or…
1
vote
0 answers

How do I translate a boolean type method into a void one in Java?

I am making a sudoku solver for a school assignment in Java, using backtracking. I have successfully solved it using a boolean solveSudoku() method but in the template provided by the teacher, the method is listed as void solveSudoku(). It clearly…
stackuser25
  • 11
  • 1
  • 1
1
vote
1 answer

Recurive Backtracking: Leet Code - Remove Boxes (Python)

I was working on this leetcode: https://leetcode.com/problems/remove-boxes/ and my answer is only slightly off for certain test cases. Any advice would be appreciated. The problem is outlined as the following: You are given several boxes with…
1
vote
0 answers

Combination Sum Backtracking Coding Problem

Given an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum to target.The same number may be chosen from candidates an unlimited number of times.The…