题解 | #表达式求值#

import java.util.LinkedList;
import java.util.List;
import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {

    private static String s = "";

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNext()) { // 注意 while 处理多个 case
            s = in.next();
        }

        result();
    }


    private static void result() {
        split();
        int result = sum(s);
        System.out.print(result);
    }

    public static void split() {

        int end = s.replaceFirst("\\)", "b").indexOf("b");
        int start = -1;
        for (int i = end - 1; i >= 0; i--) {
            char c = s.charAt(i);
            if (c == '(') {
                start = i;
                break;
            }
        }
        if (start == -1) {
            return;
        }

        String temp = s.substring(start + 1, end);
        int sum = sum(temp);
        String s1 = s.replace("(" + temp + ")", sum<0?  ("a"+(-sum)) : (sum + ""));
        s = s1;
        split();
    }

    private static int sum(String temp) {

        Node1 root = new Node1();
        Node1 tNode = new Node1();
        root.eqList.add(tNode);
        int len = temp.length();
        for (int i = 0; i < len; i++) {
            char c = temp.charAt(i);
            if (c >= '0' && c <= '9') {
                int ci = (int) c - 48;
                int d = tNode.data * 10 + (tNode.symbol ? ci : -ci);
                tNode.data = d;
                continue;
            }
            if (i == 0 && c == '-') {
                tNode.symbol = false;
                continue;
            }
            if (c == 'a') {
                tNode.symbol = !tNode.symbol;
                continue;
            }
            tNode = setNode(root, tNode, c);
        }


        return root.getResult();
    }

    private static Node1 setNode(Node1 root, Node1 t, char c) {

        if ('*' == c || '/' == c) {
            Node1 n = setNextNode(root, t);
            t.nextMultSymbol = c == '*';
            return n;
        } else if ('+' == c || '-' == c) {
            Node1 n = setEqNode(root);
            if (c == '-') {
                n.symbol = false;
            }
            return n;
        } else {
            return t;
        }
    }

    private static Node1 setNextNode(Node1 root, Node1 t) {

        Node1 n = new Node1();
        t.nextNode = n;
        return n;
    }

    private static Node1 setEqNode(Node1 root) {

        Node1 n = new Node1();
        root.eqList.add(n);
        return n;
    }


    static class Node1 {

        public int data = 0;
        public boolean symbol = true;
        public boolean nextMultSymbol = true;
        public List<Node1> eqList = new LinkedList<>();
        public Node1 nextNode = null;

        public int getEqualSum() {
            int sum = eqList.stream().mapToInt(i -> i.getResult()).sum();
            return sum;
        }

        public int getNextResult() {

            if (nextNode != null) {
                int t = data;
                while (nextNode != null) {
                    if (nextMultSymbol) {
                        t = t * nextNode.data;
                    } else {
                        t = t / nextNode.data;
                    }
                    nextNode = nextNode.nextNode;
                }

                return t;
            }
            return data;
        }

        public int getResult() {
            int res = getEqualSum() + getNextResult();
            return res;
        }
    }

}

多优化，修复bug