根据单词中的位置替换字符串中的字母

Question

我正在编写一个程序来使用英语中的字母频率来破译代码。例如，在英语中，e 是最常用的字母，它的使用率为 13%。在密码中，大约 13% 的时间也使用 a，因此 a 很可能对应于 e。然而，每个单词的首字母也有不同的频率。例如，字母“T”有 16.6% 的时间用作单词的首字母，对应于密文中的 q。这是一个链接到更多关于它http://en.wikipedia.org/wiki/Letter_frequency

我使用的基本伪代码是，

• 将密码放入字符串并删除大写字母
• 遍历文本，计算每个字母出现的时间
• 在文本中循环计算单词的每个首字母
• 创建一个类来保存字母值和该字母出现的次数
• 创建一个该类的数组，每个字母都有一个数组
• 从高到低对数组进行排序
• 用对应的字母替换首字母
• 用对应的字母替换其他字母
• 应该有可读的消息

我已经开始更换字母阶段了。我知道我可以使用替换来更改字母，但是我的问题是如何仅将每个单词的第一个字母更改为对应的字母以及替换剩余的字母，因为两者的频率不同，具体取决于它是否是第一个字母。

任何帮助都会很明显。

public class CodeCracker
{

    public CodeCracker() throws FileNotFoundException
    {
        File cipher = new File("enciphered.txt");
        Scanner cipherInput = new Scanner(cipher);

        String cipherText = "";

        //add file to string
        while(cipherInput.hasNextLine()){
            cipherText += cipherInput.nextLine(); 
        }
        cipherText = cipherText.toLowerCase();
        //count total letters

        System.out.println("~~~Original Message~~~");
        System.out.println(cipherText);


        //****Count letter Occurences****
        List<LetterOccurence> allLettersPercentage = CountLetterPercentage(cipherText);
        List<LetterOccurence> firstLetterPercentage = CountFirstLetterPercentage(cipherText);
        for(int i = 0; i <firstLetterPercentage.size(); i++){
            //System.out.println(allLettersPercentage.get(i).GetLetter() + " - " + allLettersPercentage.get(i).GetOccurence());
           System.out.println(firstLetterPercentage.get(i).GetLetter() + " - " + firstLetterPercentage.get(i).GetOccurence());
        }
         System.out.println("~~~New Message~~~");
        System.out.println(CompareAllLetters(allLettersPercentage,cipherText));
    }

    //Counts occurence of each letter in text, makes a new object with the assigned letter and the percentage
    // of the letter occuring, then sorts them from highest to lowest and returns a list array
    public List<LetterOccurence> CountLetterPercentage(String text){
        double totalLetters = 0;                        //total letters in text
        totalLetters = text.length();                   
        String indexes = "abcdefghijklmnopqrstuvwxyz";  //letters we are counting
        int[] count = new int [indexes.length()];       //array of ints for each letter   
        double[] letterPercentage = new double[indexes.length()];   //Percent of number of times the letter appears
        List<LetterOccurence> letterOccurences = new ArrayList<LetterOccurence>(indexes.length());  //list of LetterOccurence class
        //iterates through each letter and counts each occurence
        for(int i = 0; i < text.length(); i++){
            int index = indexes.indexOf(text.charAt(i));
            if (index < 0)
                continue;

            count[index]++;                             //count letter
        }
        //calculates letter percentages
        for( int i = 0; i < count.length; i++){
            if(count[i] < 1){
                continue;
            }
            //get percentage
            letterPercentage[i] = count[i] /totalLetters * 100;
            //create a class to store variables
            letterOccurences.add(new LetterOccurence(indexes.charAt(i),letterPercentage[i]));

        }
        //sort our array from highest to lowest
        Collections.sort(letterOccurences);  
        //return our array
        return letterOccurences;
    }
    public List<LetterOccurence> CountFirstLetterPercentage(String text){
        double totalLetters = 0;                        //total letters in text                  
        String indexes = "abcdefghijklmnopqrstuvwxyz";  //letters we are counting
        int[] count = new int [indexes.length()];       //array of ints for each letter   
        double[] letterPercentage = new double[indexes.length()];   //Percent of number of times the letter appears
        List<LetterOccurence> letterOccurences = new ArrayList<LetterOccurence>(indexes.length());  //list of LetterOccurence class
        String firstLetters ="";
        String[] split = text.split(" ");
        for(String value : split){
            firstLetters += value.substring(0,1);
        }
        totalLetters = firstLetters.length();
        System.out.println(firstLetters);
        //iterates through each letter and counts each occurence
        for(int i = 0; i < firstLetters.length(); i++){
            int index = indexes.indexOf(firstLetters.charAt(i));
            if (index < 0)
                continue;

            count[index]++;                             //count letter
        }
        //calculates letter percentages
        for( int i = 0; i < count.length; i++){
            if(count[i] < 1){
                continue;
            }
            //get percentage
            letterPercentage[i] = count[i] /totalLetters * 100;
            //create a class to store variables
            letterOccurences.add(new LetterOccurence(indexes.charAt(i),letterPercentage[i]));

        }
        //sort our array from highest to lowest
        Collections.sort(letterOccurences);  
        //return our array
        return letterOccurences;
    }
    public String CompareAllLetters(List<LetterOccurence> codeLetters, String code){
        //Letter Frequency order
        char[] letterFrequency = {'e','t','a','o','i','n','s','h','r','d','l','c','u','m','w','f','g','y','p','b','v','k','j','x','q','z'};

        for(int i = 0;i < codeLetters.size(); i++){

            code = code.replace(codeLetters.get(i).GetLetter(),letterFrequency[i]); 
        }
        return code;

    }
}

public class LetterOccurence implements Comparable<LetterOccurence>{
    private char letter;
    private double occurence;
    public LetterOccurence(char letter, double occurence){
        this.letter = letter;
        this.occurence = occurence;
    }
    public double GetOccurence(){
        return occurence;
    }
    public char GetLetter(){
        return letter;
    }

    public int compareTo(LetterOccurence o){
        // return (occurence - o.occurence);
        return new Double(o.occurence).compareTo(new Double(this.occurence));
    }
}

Answer 1

使cipherText 成为一个字符数组，然后在需要时遍历它并更改给定的字符。字符串是不可变的，因此您无法在创建字符串后更改其内容。从字符串中添加或减去会返回一个 完全 新字符串，而不是更改字符串的值。当你需要返回一个字符串时，只需：

return new String(cipherText);

使用String(char[] array) 构造函数。