题解 | #表达式求值#

import java.util.*;

public class Main{ public static void main(String[] srgs){ Scanner sc = new Scanner(System.in); while(sc.hasNext()){ String str = sc.nextLine(); process(str); } }

public static void process(String str){
    String s1 = str.replace("[","(");
    String s2 = s1.replace("]",")");
    String s3 = s2.replace("{","(");
    String s4 = s3.replace("}",")");
    int res = solve(s4);
    System.out.println(res);
}

public static int solve(String s){
    if(s==null||s.length()==0) return 0;
    Stack<Integer> stack = new Stack<>();
    char[] chs = s.toCharArray();
    int len = s.length(), number=0;
    char sign = '+';
    for(int i=0;i<len;i++){
        char c = chs[i];
        if(c==' ') continue;
        if(Character.isDigit(c)){
            number = number*10 + c-'0';
        }
        if(c=='('){
            int j=i+1, count=1;
            while(count>0){
                if(chs[j]==')') count--;
                if(chs[j]=='(') count++;
                j++;
            }
            number = solve(s.substring(i+1,j-1));
            i=j-1;
        }
        if(!Character.isDigit(c)||i==len-1){
            if(sign=='+'){
                stack.push(number);
            }else if(sign=='-'){
                stack.push(-1*number);
            }else if(sign=='*'){
                stack.push(stack.pop()*number);
            }else if(sign=='/'){
                stack.push(stack.pop()/number);
            }
            sign = c;
            number = 0;
        }
    }
    int ans = 0;
    while(!stack.isEmpty()){
        ans += stack.pop();
    }
    return ans;
}

}