Question

如果我们假设一个String表达式(x1(x2)(x3)(x4(x5(x6)(x7)))(x8))，如何提取特定深度的子字符串（即子表达式）？

如果搜索项为x4，则子表达式为(x4(x5(x6)(x7)))，或者如果搜索项为x5，则子表达式为(x5(x6)(x7))

Answer 1

这可能是一个非常天真的解决方案，但如果没有更多关于你完全希望实现的细节，这就满足了你的问题：

public static String getSubExpression(String expression, String search, char open, char close) {    
    int idx = expression.indexOf(open + search);

    if (idx == -1)
        return ""; //No match was found for the search term.

    int depth = 0;

    StringBuilder builder = new StringBuilder();

    //Loop over the rest of the string, looking for the terminating portion of the expression
    for (int i = idx; i < expression.length(); i++) {
        char c = expression.charAt(i);

        if (c == open) depth++; //If an open char is found, increment the depth.
        if (c == close) depth--; //If a close char is found, decrement the depth.

        builder.append(expression.charAt(i)); //append the character

        //when depth drops back to 0 or less, we know the entire expression has been parsed.
        if (depth < 1) break;
    }

    return builder.toString();
}

您可以按如下方式使用它：

String expression = "(x1(x2)(x3)(x4(x5(x6)(x7)))(x8))";
System.out.println(getSubExpression(expression, "x1", '(', ')'));
System.out.println(getSubExpression(expression, "x2", '(', ')'));
System.out.println(getSubExpression(expression, "x3", '(', ')'));
System.out.println(getSubExpression(expression, "x4", '(', ')'));
System.out.println(getSubExpression(expression, "x5", '(', ')'));
System.out.println(getSubExpression(expression, "x6", '(', ')'));
System.out.println(getSubExpression(expression, "x7", '(', ')'));
System.out.println(getSubExpression(expression, "x8", '(', ')'));

输出

(x1(x2)(x3)(x4(x5(x6)(x7)))(x8))
(x2)
(x3)
(x4(x5(x6)(x7)))
(x5(x6)(x7))
(x6)
(x7)
(x8)

Answer 2

    String source = "(x1(x2)(x3)(x4(x5(x6)(x7)))(x8))";
    String searchCriteria = "x4";

    // searching in the String assuming it is Mathematical expressions

    int searchCriteriaCount = searchCriteria.length();
    int firstMatchedCharIndex = 0;
    int lastMatchedCharIndex = 0;

    knowingIndex:
    for(int i = 0;i < source.length();i++){
        String currentSequence = source.substring(i, i+searchCriteriaCount);
        if(currentSequence.equals(searchCriteria)){
            firstMatchedCharIndex = i;
            break knowingIndex;
        }
    }

    char openingBracket = '(';
    char closingBracket = ')';
    int openingBracketsCount = 0;
    int closingBracketsCount = 0;

    char[] sourceChars = source.toCharArray();

    fullCriteria:
    for(int i = firstMatchedCharIndex-1;i<sourceChars.length;i++){
        if(sourceChars[i] == openingBracket){
            openingBracketsCount++;
        }

        if(sourceChars[i] == closingBracket){
            closingBracketsCount++;
        }

        if(openingBracketsCount == closingBracketsCount){
            lastMatchedCharIndex = i;
            break fullCriteria;
        }

    }

    String finalEquation = source.substring(firstMatchedCharIndex-1, lastMatchedCharIndex+1);

    System.out.println(finalEquation);

如何从Java中的String表达式中提取子表达式？

2 个答案:

输出