Fast algorithms are computational methods designed to solve problems efficiently, minimizing the time required to reach a solution. They are essential in computer science, as they enable quick processing of large datasets and complex calculations. Examples include sorting algorithms like QuickSort and MergeSort, which organize data swiftly, and Dijkstra's algorithm, which finds the shortest path in graphs. The efficiency of an algorithm is often measured by its time complexity, typically expressed using Big O notation. Fast algorithms can significantly improve performance in applications such as machine learning, data analysis, and cryptography, where speed is crucial for handling vast amounts of information.