题解 | #牛牛计算器#

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
     *
     *
     * @param s string字符串
     * @return int整型
     */
    public int calculate (String s) {
        // write code here

        s = s.replaceAll(" ", "");
        StringBuilder str1 = new StringBuilder();
        StringBuilder str2 = new StringBuilder();
        Stack<Integer> s1 = new Stack<>();
        Stack<Character> s2 = new Stack<>();

        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if (ch == '+' || ch == '-' || ch == '*' || ch == '/'  ) {
                str1.append(",");
                str2.append(ch);
            } else if ( ch == '(' || ch == ')') {
                str2.append(ch);
            } else {
                str1.append(ch);
                if (str2.length() == 0 || str2.length() != 0 && str2.charAt(str2.length() - 1) != '0'){
                    str2.append("0");
                }
            }
        }
        StringBuilder sb = new StringBuilder();
        String[] arr = str1.toString().split(",");
        for (String str : arr) {
            if (str != null && str.length() != 0) {
                sb.append(str + ",");
            }
        }
        arr = sb.substring(0, sb.length() - 1).split(",");
        int flag = 0;
        for (int i = 0, j = 0; i < str2.length(); i++) {
            char ch = str2.charAt(i);
            if (ch == '*' || ch == '/') {
                if (str2.charAt(i + 1) == '0') {
                    if (ch == '*') {
                        s1.add(s1.pop() * Integer.valueOf(arr[j]));
                        j++;
                        i++;
                    } else {
                        s1.add(s1.pop() / Integer.valueOf(arr[j]));
                        j++;
                        i++;
                    }
                } else {
                    s2.add(ch);
                }
            } else if (ch == '(') {
                s2.add(ch);
            } else if (ch == ')') {

                while (s2.peek() != '(') {

                    int num1 = s1.pop();
                    int num2 = s1.pop();
                    if (s2.pop() == '-') {
                        num1 = 0 - num1;
                    }
                    if (s2.peek() == '-') {
                        num2 = 0 - num2;
                        s2.pop();
                        s2.add('+');
                    }
                    s1.add(num1 + num2);
                }
                s2.pop();
                if (!s2.isEmpty() && s2.peek() == '*') {
                    s2.pop();
                    int num1 = s1.pop();
                    int num2 = s1.pop();
                    s1.add(num1 * num2);
                } else if (!s2.isEmpty() && s2.peek() == '/') {
                    s2.pop();
                    int num1 = s1.pop();
                    int num2 = s1.pop();
                    s1.add(num2 / num1);
                }

            } else if (ch == '+') {
                s2.add(ch);
            } else if (ch == '-') {
                if (i == 0 || (i - 1 >= 0 && str2.charAt(i - 1) != '0' && str2.charAt(i - 1) != ')')) {
                    s1.add(0 - Integer.valueOf(arr[j]));
                    j++;
                    i++;
                } else {
                    s2.add(ch);
                }
            } else {
                s1.add(Integer.valueOf(arr[j]));
                j++;
            }
        }
        while (!s2.isEmpty()) {

            int num1 = s1.pop();
            int num2 = s1.pop();
            if (s2.pop() == '-') {
                num1 = 0 - num1;
            }
            if (!s2.isEmpty() && s2.peek() == '-') {
                num2 = 0 - num2;
                s2.pop();
                s2.add('+');
            }
            s1.add(num1 + num2);
        }

        return s1.pop();
    }
}