题解 | #表达式求值#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     * 返回表达式的值
     * @param s string字符串 待计算的表达式
     * @return int整型
     */
    public int solve (String s) {
        LinkedList<Character> queue = new LinkedList<>();
        for(int i = 0;i<s.length();i++){
            queue.add(s.charAt(i));
        }
        return solve(queue);
        
    }
    public int solve(LinkedList<Character> queue){
        Stack<Integer> stack1 = new Stack<>();
        char sign = '+';
        int num = 0;
        while(!queue.isEmpty()){
            
            if(ch == '('){
                num = solve(queue);
            if(Character.isDigit(ch)){
                num = num * 10 + ch-'0';
            if(!Character.isDigit(ch)||queue.size()==0){
                if(sign == '-'){
                    stack1.push(-num);
                }else if(sign == '*'){
                    int num1 = stack1.pop();
                    stack1.push(num*num1);
                }else if(sign == '+'){
                    stack1.push(num);
                }
                //更新符号，数字重置
                sign = ch;
                num = 0;   
            }
            if(ch == ')'){
                break;
            }
           
        int ans = 0;
        while(!stack1.empty()){
            ans += stack1.pop();
        }
        return ans;
    }
}