java - 如何进一步优化代码？

Question

祝大家今天愉快。

我的代码可以在几秒钟内完成 Excel Pivot 的功能。然而，我的代码在不少于 30 分钟内完成了同样的事情。我对差异感到震惊!我很确定我可以优化我的代码，使它比现在快得多。任何帮助将不胜感激。

请快速查看代码。如有必要，我将详细解释它到底做了什么。谢谢你!

public void countImages(ArrayList<String> all) throws IOException {
        HashSet<String> uStrings = new HashSet<>();
        int Counter = 0;
        int C500x500 = 0;
        int C800x800 = 0;
        int C1000x1000 = 0;
        int G1000x1000 = 0;
        write("Vendor ID, Count of Images, Less than 500 x 500, Less than 800 x 800, Less than 1000 x 1000, Greater than 1000 x 1000", "ImageCount_Data");
        for (String single : all) {
            String[] linearray = single.split(",");
            uStrings.add(linearray[0]);
        }
        totallines = uStrings.size();
        completedlines = 0;
        percentage = 0;
        setPercent(0);
        for (String uString : uStrings) {
            Counter = 0;
            C500x500 = 0;
            C800x800 = 0;
            C1000x1000 = 0;
            G1000x1000 = 0;
            for (String single : all) {
                String[] linearray = single.split(",");
                if (linearray[0].equals(uString)) Counter++;
                if ((linearray[1].equals("Less than 500 x 500")) && linearray[0].equals(uString)) C500x500++;
                if ((linearray[1].equals("Less than 800 x 800")) && linearray[0].equals(uString)) C800x800++;
                if ((linearray[1].equals("Less than 1000 x 1000")) && linearray[0].equals(uString)) C1000x1000++;
                if ((linearray[1].equals("Greater than 1000 x 1000")) && linearray[0].equals(uString)) G1000x1000++;
            } //END OF 2ND FOR LOOP
            write(uString + "," + Counter + "," + C500x500 + "," + C800x800 + "," + C1000x1000 + "," + G1000x1000, "ImageCount_Data");
            completedlines++;
            percentage = (completedlines / totallines) * 100;
            setPercent(Math.round(percentage));
            Icwindow.frame.setTitle("Writing Image Count Data: " + getPercent() + "%");
        } //END OF 1ST FOR LOOP
        Icwindow.frame.setTitle("Process Cloudinary ImageCount Data");
    }

Answer 1

您正在遍历零列中所有可能的字符串，然后在该循​​环中再次遍历所有字符串。因此，您的算法是 O(n²)，而 Excel 使用更快(可能是 O(n) 摊销)算法。

你可以使用 HashMap<String, Counts>仅使用一个 for 循环而不是两个嵌套循环来跟踪计数。

Counts然后对象将包含您的类的计数，如:

class Counts {
    int c500;
    int c800;
    int c1000;
    int cOther;

    void count(String s) {
        switch(s) {
        case "Less than 500 x 500": c500++; break;
        case "Less than 500 x 500": c800++; break;
        case "Less than 500 x 500": c1000++; break;
        case "Greater than 1000 x 1000": cOther++; break;
        default: throw new AssertionError();
        }
    }
}

另一个提示:您可以通过添加 c500 + c800 + c1000 + cOther 来获取全局计数器.