java - 获取字符串中某个位置周围的单词

Question

我想获取字符串中某个位置周围的单词。例如后两个词和前两个词。

例如考虑字符串:

String str = "Hello my name is John and I like to go fishing and hiking I have two sisters and one brother.";
String find = "I";

for (int index = str.indexOf("I"); index >= 0; index = str.indexOf("I", index + 1))
{
    System.out.println(index);
}

这会写出单词“I”所在位置的索引。但我希望能够获得围绕这些位置的单词的子串。

我希望能够打印出“John and I like to”和“and hiking I have two”。

不仅应该能够选择单个单词字符串。搜索“John and”将返回“name is John and I like”。

有什么简洁、聪明的方法可以做到这一点吗？

Answer 1

单个词:

您可以使用 String's split() method 实现这一目标.这个解决方案是O(n)。

public static void main(String[] args) {
    String str = "Hello my name is John and I like to go fishing and "+
                         "hiking I have two sisters and one brother.";
    String find = "I";

    String[] sp = str.split(" +"); // "+" for multiple spaces
    for (int i = 2; i < sp.length; i++) {
        if (sp[i].equals(find)) {
            // have to check for ArrayIndexOutOfBoundsException
            String surr = (i-2 > 0 ? sp[i-2]+" " : "") +
                          (i-1 > 0 ? sp[i-1]+" " : "") +
                          sp[i] +
                          (i+1 < sp.length ? " "+sp[i+1] : "") +
                          (i+2 < sp.length ? " "+sp[i+2] : "");
            System.out.println(surr);
        }
    }
}

输出:

John and I like to
and hiking I have two

多词:

当 find 是一个多词时，Regex 是一个很好的干净的解决方案。但是，由于其性质，它会错过 周围的单词也匹配 find 的情况(参见下面的示例)。

下面的算法处理所有情况(所有解决方案的空间)。请记住，由于问题的性质，最坏情况下的解决方案是 O(n*m) ^{(n 为 str 的长度和 m 是 find 的长度)}。

public static void main(String[] args) {
    String str = "Hello my name is John and John and I like to go...";
    String find = "John and";

    String[] sp = str.split(" +"); // "+" for multiple spaces

    String[] spMulti = find.split(" +"); // "+" for multiple spaces
    for (int i = 2; i < sp.length; i++) {
        int j = 0;
        while (j < spMulti.length && i+j < sp.length 
                                  && sp[i+j].equals(spMulti[j])) {
            j++;
        }           
        if (j == spMulti.length) { // found spMulti entirely
            StringBuilder surr = new StringBuilder();
            if (i-2 > 0){ surr.append(sp[i-2]); surr.append(" "); }
            if (i-1 > 0){ surr.append(sp[i-1]); surr.append(" "); }
            for (int k = 0; k < spMulti.length; k++) {
                if (k > 0){ surr.append(" "); }
                surr.append(sp[i+k]);
            }
            if (i+spMulti.length < sp.length) {
                surr.append(" ");
                surr.append(sp[i+spMulti.length]);
            }
            if (i+spMulti.length+1 < sp.length) {
                surr.append(" ");
                surr.append(sp[i+spMulti.length+1]);
            }
            System.out.println(surr.toString());
        }
    }
}

输出:

name is John and John and
John and John and I like