Practice
Resources
Contests
Online IDE
New
Free Mock
Events New Scaler
Practice
Improve your coding skills with our resources
Contests
Compete in popular contests with top coders
logo
Events
Attend free live masterclass hosted by top tech professionals
New
Scaler
Explore Offerings by SCALER

Backtracking

Go to Problems

Level 1

Jump to Level 2

Level 2

Jump to Level 3

Level 3

Jump to Level 4

Level 4

Jump to Level 5

Level 5

Jump to Level 6

Level 6

Jump to Level 7

Level 7

Jump to Level 8

Level 8

Be a Code Ninja!

Maze Traversal Algorithm Using Backtracking

Backtracking is trying out all possibilities using recursion, exactly like bruteforce.
Suppose you have to make a series of decisions, among various choices, where :

  * You don’t have enough information to know what to choose
  * Each decision leads to a new set of choices
  * Some sequence of choices (possibly more than one) may be a solution to your problem

Backtracking is a methodical way of trying out various sequences of decisions, until you find one that “works”.

Lets look at an example to explain this further.

Given a maze, find if a path from start to finish

At each intersection, you have to decide between three or fewer choices:

    * Go straight
    * Go left
    * Go right

You don’t have enough information to choose correctly. Each choice leads to another set of choices. One or more sequences of choices may (or may not) lead to a solution.
So, you explore each option thoroughly and once you cannot find a solution using the option selected, you come back and try one of the remaining options.

Backtracking Pseudocode

A pseudocode for the above question would be :

        boolean pathFound(Position p) {
            if (p is finish) return true;
            
            foreach option O from p {
                boolean isThereAPath = pathFound(O);
                if (isThereAPath) return true; // We found a path using option O
            }
            // We have tried all options from this position and none of the options lead to finish. 
            // Hence there is no solution possible to finish
            return false;
        }

In general, the usual pseudocode for any backtracking solution is :

        boolean solve(Node n) {
            if n is a goal node, return true
            
            foreach option O possible from n {
                if solve(O) succeeds, return true
            }
            return false
        }

Now, head over to the assignments, and try out some of the problems. Most of them involve backtracking.

Serious about Learning Programming ?

Learn this and a lot more with Scaler Academy's industry vetted curriculum which covers Data Structures & Algorithms in depth.

Backtracking Problems

Subsets
Problem Score Companies Time Status
All Possible Combinations 200 36:16
Subset 250 61:56
Combination Sum 300 62:41
Combination Sum II 300 42:04
Combinations 300 46:09
Subsets II 300 41:22
Maths and backtracking
Problem Score Companies Time Status
Maximal String 200
65:19
Kth Permutation Sequence 350 78:59
Gray Code 350
58:55
Bruteforce builder
Problem Score Companies Time Status
Letter Phone 250 53:36
Palindrome Partitioning 300 68:22
Generate all Parentheses II 350
52:54
Permutations
Problem Score Companies Time Status
Permutations 350 39:38
Game solving
Problem Score Companies Time Status
NQueens 550 74:40
Sudoku 700 70:45
Excel at your interview with Masterclasses Know More
Certificate included
What will you Learn?
Free Mock Assessment
Fill up the details for personalised experience.
Phone Number *
OTP will be sent to this number for verification
+91 *
+91
Change Number
Graduation Year *
Graduation Year *
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
*Enter the expected year of graduation if you're student
Current Employer
Company Name
College you graduated from
College/University Name
Job Title
Job Title
Engineering Leadership
Software Development Engineer (Backend)
Software Development Engineer (Frontend)
Software Development Engineer (Full Stack)
Data Scientist
Android Engineer
iOS Engineer
Devops Engineer
Support Engineer
Research Engineer
Engineering Intern
QA Engineer
Co-founder
SDET
Product Manager
Product Designer
Backend Architect
Program Manager
Release Engineer
Security Leadership
Database Administrator
Data Analyst
Non Coder
Other
Please verify your phone number
Edit
Resend OTP
By clicking on Start Test, I agree to be contacted by Scaler in the future.
Already have an account? Log in
Free Mock Assessment
Instructions from Interviewbit
Start Test