[英]Reverse the words in a sentence but not punctuation using recursion
How to reverse the words in a sentence, but not punctuation using recursion.如何使用递归来反转句子中的单词,而不是标点符号。 The sentence is said to use punctuation marks: ,.?!据说该句子使用标点符号:,.?!
Input: "Jack, come home!"输入:“杰克,回家!”
Output: "home, come Jack!" Output:“回家,杰克来了!”
Now I have somehow managed to complete the task correctly but without using recursion.现在我以某种方式设法正确完成了任务,但没有使用递归。 How should I convert this work to use recursion to solve the problem?我应该如何将这项工作转换为使用递归来解决问题?
Here's the method:这是方法:
public static StringBuilder reverseSentenceWithPunctuation(String sentence, int i) {
String[] parts = sentence.split(" ");
StringBuilder newSentence = new StringBuilder();
Map<Integer, Character> punctuationMap = new HashMap<>();
for (int j = 0; j < parts.length; j++) {
if (parts[j].endsWith(",") || parts[j].endsWith(".") || parts[j].endsWith("!") || parts[j].endsWith("?")) {
char lastSymbol = parts[j].charAt(parts[j].length()-1);
punctuationMap.put(j, lastSymbol);
String changedWord = parts[j].replace(String.valueOf(lastSymbol), "");
parts[j] = changedWord;
}
}
for (int j = parts.length-1; j >= 0; j--) {
newSentence.append(parts[j]);
if (punctuationMap.containsKey(i)) {
newSentence.append(punctuationMap.get(i));
newSentence.append(" ");
} else
newSentence.append(" ");
i++;
}
return newSentence;
}
Thanks in advance!提前致谢!
To implement this task using recursion, a pattern matching the first and the last words followed by some delimiters should be prepared:为了使用递归来实现这个任务,应该准备一个匹配第一个和最后一个单词的模式,然后是一些分隔符:
word1 del1 word2 del2 .... wordLast delLast
In case of matching the input the result is calculated as:在匹配输入的情况下,结果计算如下:
wordLast del1 REVERT(middle_part) + word1 delLast
Example implementation may be as follows (the words are considered to contain English letters and apostrophe '
for contractions):示例实现可能如下(单词被认为包含英文字母和撇号'
用于缩写):
static Pattern SENTENCE = Pattern.compile("^([A-Za-z']+)([^A-Za-z]+)?(.*)([^'A-Za-z]+)([A-Za-z']+)([^'A-Za-z]+)?$");
public static String revertSentence(String sentence) {
Matcher m = SENTENCE.matcher(sentence);
if (m.matches()) {
return m.group(5) + (m.group(2) == null ? "" : m.group(2))
+ revertSentence(m.group(3) + m.group(4)) // middle part
+ m.group(1) + (m.group(6) == null ? "" : m.group(6));
}
return sentence;
}
Tests:测试:
System.out.println(revertSentence("Jack, come home!"));
System.out.println(revertSentence("Jack, come home please!!"));
System.out.println(revertSentence("Jane cried: Will you come home Jack, please, don't go!"));
Output: Output:
home, come Jack!
please, home come Jack!!
go don't: please Jack home come you, Will, cried Jane!
I don't think this is a good case for a recursive function, mainly because you need 2 loops.我认为这不是递归 function 的好案例,主要是因为您需要 2 个循环。 Also, in general, iterative algorithms are better performance-wise and won't throw a stackoverflow exception.此外,一般来说,迭代算法在性能方面更好,并且不会引发 stackoverflow 异常。
So I think the main reasons to work with recursive functions is readability and easiness, and honestly, in this case, I think it isn't worth it.所以我认为使用递归函数的主要原因是可读性和易用性,老实说,在这种情况下,我认为它不值得。
In any case, this is my attempt to convert your code to a recursive function.无论如何,这是我将您的代码转换为递归 function 的尝试。 As stated before, I use 2 functions because of the 2 loops.如前所述,由于有 2 个循环,我使用了 2 个函数。 I'm sure there is a way to achieve this with a single function that first loads the map of punctuations and then compose the final String, but to be honest that would be quite ugly.我确信有一种方法可以使用单个 function 来实现这一点,它首先加载 map 的标点符号,然后组成最终的字符串,但老实说这会很丑陋。
import java.util.*;
import java.util.stream.*;
public class HelloWorld{
static Character[] punctuationCharacters = {',','.','!'};
public static void main(String []args){
System.out.println(reverseSentenceWithPunctuation("Jack, come home!"));
}
private static String reverseSentenceWithPunctuation(String sentence) {
String[] parts = sentence.split(" ");
return generate(0, parts, extractPunctuationMap(0, parts));
}
private static Map<Integer, Character> extractPunctuationMap(int index, String[] parts){
Map<Integer, Character> map = new HashMap<>();
if (index >= parts.length) {
return map;
}
char lastSymbol = parts[index].charAt(parts[index].length() - 1);
if (Arrays.stream(punctuationCharacters).anyMatch(character -> character == lastSymbol)) {
parts[index] = parts[index].substring(0, parts[index].length() - 1);
map = Stream.of(new Object[][] {
{ index, lastSymbol}
}).collect(Collectors.toMap(data -> (Integer) data[0], data -> (Character) data[1]));
}
map.putAll(extractPunctuationMap(index + 1, parts));
return map;
}
private static String generate(int index, String[] parts, Map<Integer, Character> punctuationMap) {
if (index >= parts.length) {
return "";
}
String part = index == 0? " " + parts[index] : parts[index];
if (punctuationMap.containsKey(parts.length -1 - index)) {
part += punctuationMap.get(parts.length -1 - index);
}
return generate(index + 1, parts, punctuationMap) + part;
}
}
In pseudocode maybe something like that:在伪代码中可能是这样的:
(a). (一个)。 get the first word得到第一个词
(b). (b)。 get the last word得到最后一句话
(if there is a punctuation after the first or last word, leave it there) (如果第一个或最后一个单词后有标点符号,请留在那里)
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