java.lang.StringIndexOutOfBounds改进

Question

public class DuplicateLetters {
    
    // CW2.2 Lab-Group-06 Question 5
    // You are given two non-empty strings source and target, all lowercase letters, from a user.
    // The user intends to type the string given in target.
    // However, due to using an old keyboard,
    // when the user was typing, a number characters may be duplicated, and typed one or more times.
    // The source is what the user actually typed, which may or may not be the intended target.
    // Return true if and only if it is possible that some characters of target have been duplicated in source,
    // while the user intended to type the target string.
    // You must use String methods in lecture notes.
    // You must NOT use StringBuilder or Regular Expression methods.
    
    public static boolean duplicateLetters(String source, String target) {
        boolean test = false;
        
        for(int i=0; i<source.length(); i++) {
            for(int j=i; j<target.length(); j++) {
                if(Character.toString(source.charAt(i)).equals(Character.toString(target.charAt(j)))) {
                    test = true;
                }
                else {
                    test = false;
                    j--;    
                }
                i++;
            }
        }
        return test;
    }
    
    public static void main(String[] args) {
        
        System.out.println(duplicateLetters("andddrew", "andrew"));
        // true, there are duplicated letters typed
        
        System.out.println(duplicateLetters("lllejiiee", "leejie"));
        // false, note the initial letter e
        // there is only one initial e in the source, whereas there is a double initial ee in the target
        
        System.out.println(duplicateLetters("cherry", "cherry"));
        // true, no duplicated letters typed this time
    }

这是我为这个问题编写的代码，但是它不断地得到java.lang.StringIndexOutOfBounds错误。所以，我想知道我的代码有什么问题，以及如何改进它。

Answer 1

这是一个正确的运行版本。注意，您还需要检查不匹配的新字符是否与最后一个目标匹配。否则duplicateLetters("axbc", "abc");就会失败。(这仍将发生在ruhul已经提出的索引修正中)。

    public static boolean duplicateLetters(String source, String target) {
        int i = 0;
        char lastTargetChar = target.charAt(0);
        for(int j=0; j<target.length(); j++) {
            while ( source.charAt(i) != target.charAt(j)) {
                // we only go in here if the char in source is wrong, thus assume a dupe, but check if it's a dupe!
                if (lastTargetChar != source.charAt(i)) {
                    return false;
                }
                i++;
                if (i >= source.length()) {
                    return false;
                }
            }
            // if we end here, source char was found ok, so remember last char and go to next char in source
            lastTargetChar = target.charAt(j);
            i++;
        }
        return true;
    }

优化：

通过

1. 循环，可以更容易地检查目标中的双字母(例如，“字母”，并在出现问题时立即执行循环。您不需要继续进行，结果在任何情况下都是正确的。

Answer 2

当i的值超出发生的source.length异常时，您将在内循环中增加值i。

for(int j=i; j<target.length(); j++) {
            if(Character.toString(source.charAt(i)).equals(Character.toString(target.charAt(j)))) {
                test = true;
            }
            else {
                test = false;
                j--;    // you don't need to decrement the value of j.
            }
            i++; // problematic code.
        }

若要修复此问题，请在比较或中断循环之前添加检查。例如：

       ...
       i++; // break the loop so that i remains consistent.
       if(i>=source.length()) break;

也是你的逻辑太复杂和错误。由于修复这些错误超出了范围，所以您应该自己找到它(作业) :P.