TAILIEUCHUNG - HandBooks Professional Java-C-Scrip-SQL part 165

Tham khảo tài liệu 'handbooks professional java-c-scrip-sql part 165', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | o Data can be accessed only by a unique index number not an arbitrary key The distribution counting sort Chapter and o Excellent time efficiency proportional to number of keys o Predictable timing o Extra memory needed for copy of pointer or data depending on implementation o Appropriate for sorting a few hundred or more keys o Each type of key to be sorted must be handled separately Caching Chapter o See entry in Figure ioopt Some Thoughts on the Future Although many managers might wish it otherwise the writing of efficient computer programs will always be an art not a science. This may appear to be a rash statement but I think time will prove me correct. Of course if I am wrong I am following a rich tradition according to Arthur C. Clarke s Law if a distinguished elderly scientist defined as over 30 years old says that something is possible he is almost always right if he says that something is impossible he is almost always However I feel I am on reasonably firm ground. The main reason is that as demonstrated by Goedel s Proof no automatic procedure can discover all of the true statements in a consistent axiomatic system such as the behavior of a programmable This implies that the development of new algorithms will always be an adventure. A fine example of this is the optimization in Chapter in which I discovered that I could replace 16-bit occurrence counts with 4-bit indexes and actually speed up the operation of the program at the same time I d like to see the optimizing compiler that could figure that out Obviously such unpredictability can be quite expensive. While other engineering professionals such as structural engineers routinely estimate the time and money required for their projects to within a few percent software engineers are not nearly so accurate. In fact overruns of hundreds of percent are not uncommon. Why is this so Why Johnny Can t Estimate The answer is quite simple once a .

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