#     
## What is backtracking?

**Backtracking** includes deciding on the simplest choice out of many possibilities. We first select a choice and back down from it if we attain a kingdom in which that particular choice no longer provides the desired solution. 

We repeat that procedure and go through all of the available options until we find the preferred solution. 

#      
## Algorithms that use backtracking

Some algorithms that use backtracking include:

1. N-queens problem
2. Graph coloring
3. Crosswords
4. Rat in the maze

#      
## Recursion vs. backtracking

**Recursion** involves a function calling itself until it reaches the base case.

Backtracking uses recursion to discover all of the possibilities until we get the best end result for the problem.



#     
## Code

The code below is an example of finding all of the possible arrangements of a given set of letters.

def permutation(list, res):
   if list == 1:
      return res
   else:
      return [ 
         y + x
         for y in permutation(1, res)
         for x in permutation(list - 1, res)
      ]
print(permutation(1, ["a","b","c"]))
print(permutation(2, ["a","b","c"]))

#     
## Explanation

When we select a pair, we use backtracking to see if that particular pair was previously created.
The pair is added to the answer list if it hasn't already been formed; otherwise, it is ignored. 

What is backtracking in Python?

Backtracking involves making choices and retracting them if they don't lead to solutions. Used in problems like the N-queens, graph coloring, and more.