The book defines complexity as a numerical function T (n)-the relationship between time and input size n, as one of the basic ideas of computer science. The computational complexity is categorized by algorithm based on its nature and function. The (computational) complexity of the algorithm is a measurement of the ratio of computational resources (time and space) consumed when a particular algorithm is running. For these issues, the book tries to locate heuristic algorithms which can almost explain the problem and operate in a reasonable timeframe. Different kinds of algorithms are described such as graph and network algorithms, algebraic algorithms, parallel algorithms and randomized algorithms.