Question

我的任务是创建执行以下操作的方法getCharAfterNthOccurance（String text，int n，String target）：

/**
* If n is not positive, throws an IllegalArgumentException.
* 
* Otherwise, returns the character that follows the nth occurrence of the
* target inside the text.
* 
* If the target does not occur n times within the text, or if the nth
* occurrence is not followed by a character, throws NoSuchElementException.
*/

不使用任何.substring方法。这是我到目前为止的代码：

public static char getCharAfterNthOccurrence (String text, int n, String target)
{
    // Your implementation goes here.  You will find the two-parameter .indexOf
    // method on strings very helpful.  Do not use any of the .substring methods, 
    // or your program will be too slow.
    if (target.length()>=text.length())
    {
        throw new NoSuchElementException();
    }
    if (n<=0 || text.length()==0)
    {
        throw new IllegalArgumentException();
    }
    if (n>text.length()+target.length())
    {
        throw new NoSuchElementException();
    }
    if (nthOccurrence(text,target,n)==-1)
    {
        throw new NoSuchElementException();
    }
    if (target.equals(""))
    {
        return text.charAt(n-1);
    }
    if (n == 1)
    {
        return text.charAt(text.indexOf(target)+target.length());
    }
    return text.charAt(nthOccurrence(text,target,n)-1); 
}
public static int nthOccurrence(String str, String c, int n)
{
    int pos = str.indexOf(c);
    while (n-- > 0 && pos != -1)
    {
        pos = str.indexOf(c, pos+1);
    }
    return pos;
}

以下是一些测试用例：

@Test
public void testGetCharAfterNthOccurrence ()
{
    assertEquals('a', getCharAfterNthOccurrence("aaaaab", 1, "a"));
    assertEquals('a', getCharAfterNthOccurrence("aaaaab", 2, "a"));
    assertEquals('a', getCharAfterNthOccurrence("aaaaab", 3, "a"));
    assertEquals('a', getCharAfterNthOccurrence("aaaaab", 4, "a"));
    //assertEquals('b', getCharAfterNthOccurrence("aaaaab", 5, "a"));
    assertEquals('d', getCharAfterNthOccurrence("abcdefabcabczabcc", 1, "abc"));
    // assertEquals('a', getCharAfterNthOccurrence("abcdefabcabczabcc", 2, "abc"));
    assertEquals('z', getCharAfterNthOccurrence("abcdefabcabczabcc", 3, "abc"));        
    // assertEquals('d', getCharAfterNthOccurrence("abcDABCd", 1, "ABC"));
}

被注释掉的那些（//）是目前正在失败的那些，我不知道如何继续。第一个失败的测试用例获得NoSuchElementException，第二个失败的测试用例期望得到＆lt; 99＆gt;但收到＆lt; 97＆gt;，第三个失败的测试用例得到NoSuchElementException可能是因为它正在寻找大写字母而没有找到它们。有什么建议吗？

在第N次出现字符串方法后，使用我的查找字符失败一个测试用例

0 个答案: