用 Java 生成字母序列

Question

我正在开始编程，我有一个生成字母序列的作业。在构造函数中，我们有一个输入，每次调用方法 next() 时都会返回序列中的下一个值。

"","a","b","c",....."z","A","B",......"Z","aa","bb",.....,"zz",.....
if input is:
If the current string is:"z",so after calling next(),we get "A";
If the current string is:"Z",so after calling next(),we get "aa";
If the current string is:"az",so after calling next(),we get "ba";
If the current string is:"ZZZZZZ",so after calling next(),we get "aaaaaaa";

代码分配网在这里：

import  java.util.Iterator;

public class StringIterator implements Iterator<String> {

    //Complete the following methods
    public StringIterator(String start){
        // task 0
        throw new UnsupportedOperationException("Delete this line and implement this function");
    }

    public boolean hasNext(){
        // task 0
        //assume string length()<Integer. MAX_VALUE
       return true;
    }
    public String next(){
        // task 0
        throw new UnsupportedOperationException("Delete this line and implement this function");
    }
}

Answer 1

想法：用你的字母表准备一个字符串 A：“abc...ABC..Z”，并准备一个“增加”函数，给定 A 中的一个字符，返回以下字符。

初始化器将原始字符串设置在变量“s”中；然后 next() 获取“s”，检查最后一个字符，并对该字符调用“increase”函数。然后用结果替换字符串的最后一个字符。但是...如果新的字符是 A 的第一个，那么您还需要“增加”“s”中的下一个字符，依此类推。直到到达字符串的末尾：在这种情况下，只需添加第一个字符字母表的。

如果可以的话，您可以为此执行递归函数。否则，您可以使用初始化为字符串长度的索引“i”，并在需要获取字符串中的前一个字符时将其移回一个位置。

/**
 *
 */
package it.mixedstuff;

import java.util.Iterator;
import java.util.NoSuchElementException;;

/**
 * @author samuele m.
 *
 */
public class StringIterator implements Iterator<String>
{
    private static final String A = "abcABC";
    private String s;

    // Complete the following methods
    public StringIterator(String start)
    {
        s = start;
    }

    private char increase(char c)
    {
        int k = A.indexOf(c);
        if (k == -1) {
            throw new RuntimeException("Unsupported char");
        }
        k = (k + 1) % A.length();
        return A.charAt(k);
    }

    private char firstChar()
    {
        return A.charAt(0);
    }

    private boolean isFirst(char ch)
    {
        return (ch == firstChar());
    }

    public boolean hasNext()
    {
        return A.length() < Integer.MAX_VALUE;
    }

    public String next()
    {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        int i = s.length();
        while (--i >= 0) {
            // get char at position A[i]
            char c = s.charAt(i);
            // return the following one
            c = increase(c);
            // replace the char in the string
            s = s.substring(0, i) + c + s.substring(i + 1);
            // have we ended?
            if (!isFirst(c)) {
                return s;
            }
        }
        // if string is ended, we need to add the first char
        if (i < 0) {
            s = firstChar() + s;
        }
        return s;
    }

    public static void main(String[] args)
    {
        String base = "Bc";
        StringIterator s = new StringIterator(base);
        System.out.println("We start with " + base);
        for (int i = 0; i < 20; i++) {
            String n = s.next();
            System.out.println("Then there is " + n);
        }
    }

}