What Is an Algorithm?

In the context of computer science, an algorithm is a finite sequence of well-defined, computer-implementable instructions. In short, an algorithm is:

Defined: there is a specific sequence of steps that performs a task
Unambiguous: there is a "correct" and "incorrect" interpretation of the steps
Implementable: it can be executed using software and hardware

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Algorithms are usually written in "pseudocode" (pronounced "sue-dough-code") because an algorithm is a higher-level description of a solution to a problem. An algorithm doesn't care if it's implemented in Python, Go, TypeScript, or (gasp) Java. Pseudocode is just plain English that describes the steps of the algorithm.

Here's some pseudocode for a mystery algorithm:

Start with an original string called S and a new empty string called R.
Loop through S from its last character to its first character, and for each one, add it to the end of R.
Once you’ve processed all the characters, return R.