java 表达式评估 INFIX 带括号和使用递归的 DMAS 规则

Question

这是我在堆栈溢出中找到的代码，但它不处理 brckets 需要帮助

public static int evaluateE(String s) {
//Base case

    if (!s.contains("+") && !s.contains("-") && !s.contains("*") && !s.contains("/")) {
        return Integer.parseInt(s);
    }

这里它首先检查优先级 + ,- 然后 *,/但它不检查括号和圆括号

    int i;
// search for '+' and '-' first

    for (i = s.length() - 1; i >= 0; i--) {
        if (s.charAt(i) == '+' || s.charAt(i) == '-') {
            break;
        }
    }
    if (i < 0) {
// if '+' and '-' were not found, search for '*' and '/'

        for (i = s.length() - 1; i >= 0; i--) {
            if (s.charAt(i) == '*' || s.charAt(i) == '/') {
                break;
            }
        }
    }

    String r1 = s.substring(0, i);
    String r2 = s.substring(i + 1, s.length());

    int result = 0;

    switch (s.charAt(i)) {
        case '+':
            result = evaluateE(r1) + evaluateE(r2);
            break;
        case '-':
            result = evaluateE(r1) - evaluateE(r2);
            break;
        case '*':
            result = evaluateE(r1) * evaluateE(r2);
            break;
        case '/':
            int right = evaluateE(r2);
            if (right == 0) //if denominator is zero
            {
                System.out.println("Invalid divisor");
                System.exit(1);
            } else {
                result = evaluateE(r1) / right;
            }
            break;
    }
    return result;

}

Answer 1

也许这有效...

public static int evaluateE(String s) {
    //Base case
    if (!s.contains("+") && !s.contains("-") && !s.contains("*") && !s.contains("/")) {
        return Integer.parseInt(s);
    }


    // iterate over string when encounter parentheses evaluate expression inside
    for(int j = 0; j < s.length(); j++){
        if (s.charAt(j) == ')'){
            int k = j;


            // go back to left parentheses
            while (s.charAt(k) != '(')
                k--;

            String left = s.substring(0,k);
            String inparen = Integer.toString(evaluateE(s.substring(k+1,j)));
            String right = s.substring(j+1,s.length());


            s = left + inparen + right;
            j = left.length() + inparen.length()-1;
        }

    }


    int i;
    // search for '+' and '-' first

    for (i = s.length() - 1; i >= 0; i--) {
        if (s.charAt(i) == '+' || s.charAt(i) == '-') {
            break;
        }
    }
    if (i < 0) {
    // if '+' and '-' were not found, search for '*' and '/'

        for (i = s.length() - 1; i >= 0; i--) {
            if (s.charAt(i) == '*' || s.charAt(i) == '/') {
                break;
            }
        }
    }

    String r1 = s.substring(0, i);
    String r2 = s.substring(i + 1, s.length());

    int result = 0;

    switch (s.charAt(i)) {
        case '+':
            result = evaluateE(r1) + evaluateE(r2);
            break;
        case '-':
            result = evaluateE(r1) - evaluateE(r2);
            break;
        case '*':
            result = evaluateE(r1) * evaluateE(r2);
            break;
        case '/':
            int right = evaluateE(r2);
            if (right == 0) {
                System.out.println("Invalid divisor");
                System.exit(1);
            }
            else result = evaluateE(r1) / right;
            break;
    }
    return result;
}

public static void main(String[] args) {
    System.out.println(evaluateE("4*(3*(6+6)+7)"));

}

在main中输入“4*(3*(6+6)+7)”

输出:

172