Recursion is a programming technique where a function calls itself in order to solve smaller instances of the same problem. It is a powerful concept in programming that allows for elegant solutions to problems that can be broken down into smaller, similar sub-problems.
In recursion, a function solves a problem by breaking it down into smaller, simpler instances of the same problem. Each recursive call works on a smaller subset of the original problem until a base case is reached, which is a problem small enough to be solved without further recursion. The results of the base cases are then combined to produce the final result.
Example (Factorial in Python):
def factorial(n):
if n == 0:
return 1
else:
return n * factorial(n - 1)
result = factorial(5)
print(result) # Output: 120
In this example, the factorial function calculates the factorial of a number n by recursively calling itself with n-1 until it reaches the base case of n == 0.