I told the Founders Forum two weeks ago that the last computer program I wrote was a Sudoku solver, written in C++ several years ago (http://bit.ly/1DMK5Zk). Someone asked me for it. Here is the source code, the exe file, and a sample printout - http://bit.ly/1zAXbua
The program is pretty basic: it runs at the command prompt, in a DOS window. Type in the data line by line (e.g. 1-3-8---6), then the solver will print out the solution (or all the solutions if there are several), the number of steps the program took searching for the solution, plus some search statistics.
For techies: the program does a backtrack search, choosing the next cell to guess which minimises the fanout.
Here’s a question for those reading the source code: if x is an (binary) integer, what does (x & -x) compute?
Hope you have fun playing with this. Please tell me if you find any bugs! – LHL
#SmartNation
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Answer: As several of you noted, (x & –x) returns the least significant ‘1’ bit of x, i.e. the highest power of two that divides x. This assumes two’s complement notation for negative numbers, as some of you also pointed out. e.g. if x=12 (binary 1100), then (x & -x) = 4 (binary 100). I didn’t invent this; it is an old programming trick. :)
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Update: A few people suggested that I add a licence to the code. Have added it in the Google Drive folder.
two complement 在 【DSE ICT 概念速成】 快速二補碼計算：正負轉換、加減數 的八卦
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