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copied!<p>Like Max, my strong suspicion was that the slowness in Go was related to poor I/O performance. I tested this hypothesis:</p> <pre><code>package main import "fmt" import "os" import "time" func main(){ now := time.Now() input,_ := os.Open("testing/test_cases.txt") defer input.Close() output,_ := os.Create("testing/Goutput.txt") defer output.Close() var ncases int var p float64 fmt.Fscanf(input,"%d",&ncases) fmt.Println("Opened files in ", time.Since(now), "seconds") now = time.Now() cases := make([]float64, ncases) fmt.Println("Made array in ", time.Since(now), "seconds") now = time.Now() for i := 0; i < ncases; i++ { fmt.Fscanf(input,"%f",&cases[i]) } fmt.Println("Read data in ", time.Since(now), "seconds") now = time.Now() for i := 0; i < ncases; i++ { p = cases[i] if p >= 0.5 { cases[i] = 10000 * (1-p) * (2*p-1) + 10000 } else { cases[i] = p*(1-2*p)*10000 + 10000 } } fmt.Println("Processed data in ", time.Since(now), "seconds") now = time.Now() for i := 0; i < ncases; i++ { fmt.Fprintln(output, cases[i]) } fmt.Println("Output processed data in ", time.Since(now), "seconds") } </code></pre> <p>Running it produced this output:</p> <pre> Opened files in 2.011228ms seconds Made array in 109.904us seconds Read data in 4.524544608s seconds Processed data in 10.083329ms seconds Output processed data in 1.703542918s seconds </pre> <p>So it appears that on my machine, all of the math occurs in about 10ms, but the I/O is slow, confirming the hypothesis. As pointed out by Janne in the comments, there are likely faster options than <code>fmt</code>.</p> <p><strong>Update:</strong> For example, wrapping <code>input</code> and <code>output</code> with <code>bufio</code>'s Readers and Writers:</p> <pre><code>binput := bufio.NewReader(input) boutput := bufio.NewWriter(output) </code></pre> <p>and using <code>binput</code> and <code>boutput</code> for buffered I/O, your original version runs in 2.1 seconds on my machine, somewhat faster than Python's 2.7.</p> <p><strong>Update 2:</strong> I noticed that I was getting different results by just switching to buffered I/O.</p> <ol> <li><p>It turns out that you also need to adjust your format strings to include the <code>\n</code>, as you do in the C version. I think this is actually more correct either way, but it looks like you can get away with it while unbuffered.</p></li> <li><p>It's also important to <code>Flush()</code> your buffered output, which I did but didn't mention before.</p></li> </ol> <p>Here's my complete buffered solution:</p> <pre><code>package main import "fmt" import "os" import "bufio" import "time" func main(){ now := time.Now() nbinput, _ := os.Open("testing/test_cases.txt") defer nbinput.Close() nboutput, _ := os.Create("testing/Goutput.txt") defer nboutput.Close() binput := bufio.NewReader(nbinput) boutput := bufio.NewWriter(nboutput) var ncases int var gain, p float64 fmt.Fscanf(binput,"%d\n",&ncases) for i := 0; i < ncases; i++ { fmt.Fscanf(binput, "%f\n", &p) if p >= 0.5 { gain = 10000 * (1-p) * (2*p -1) } else { gain = p*(1-2*p)*10000 } fmt.Fprintln(boutput, gain+10000) } boutput.Flush() fmt.Println("Took ", time.Since(now), "seconds") } </code></pre>

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