计算器的功能

package Leecode;

import java.util.ArrayDeque;
import java.util.Deque;

public class Calculator {
    public static double calculate(String s) {
        int n = s.length();
        if (n == 0) return 0;
        double temp = 0;
        double result = 0;
        Character sign = '+';
        Deque<Double> deque = new ArrayDeque<>();
        for (int i = 0; i < n; i++) {
      //小数点
            if (s.charAt(i) == '.') {
                int j = i + 1;
                double temp1 = 0;
                while (j < n && Character.isDigit(s.charAt(j))) {
                    temp1 = temp1 * 10 + s.charAt(j) - '0';
                    //System.out.println(temp1);
                    j++;
                }
                int length = j - i - 1;
                temp = temp + temp1 / Math.pow(10, length);
                //System.out.println(temp);
                if (j != n) i = j;
                else {
                    i = j - 1;
                    if (sign == '+') {
                        deque.push(temp);
                    } else if (sign == '-') {
                        deque.push(-temp);
                    } else if (sign == '*') {
                        deque.push(deque.pop() * temp);
                    } else if (sign == '/') {
                        deque.push(deque.pop() / temp);
                    }
                    break;
                }
            }
            if (i < n && Character.isDigit(s.charAt(i))) {
                temp = temp * 10 + s.charAt(i) - '0';
            }
        //考虑运算一个负数 如2*-2.5,这时候的-就不能看成运算符
            if (i<n-1&&i>0&&s.charAt(i)=='-' &&!Character.isDigit(s.charAt(i-1))){
                int j =i+1;
                double temp1 = 0;
                while (j < n && (Character.isDigit(s.charAt(j))||s.charAt(j)=='.')) {
                    while (j<n&&Character.isDigit(s.charAt(j))) {
                        temp1 = temp1 * 10 + s.charAt(j) - '0';
                        j++;
                    }
                    //System.out.println(temp1);
                    if (j<n-1&&s.charAt(j)=='.'){
                        int k = j + 1;
                        double temp2 = 0;
                        while (k < n && Character.isDigit(s.charAt(k))) {
                            temp2 = temp2 * 10 + s.charAt(k) - '0';
                            //System.out.println(temp1);
                            k++;
                        }
                        int length = k-j-1;
                        temp1 = temp1 + temp2/Math.pow(10,length);
                        //System.out.println(temp1);
                        j = k;
                    }
                }
                temp = -temp1;
                i = j-1;
            }
          //运算符  
            if (i < n && (!Character.isDigit(s.charAt(i))) || i == n - 1) {
                //System.out.println(sign);
                if (sign == '+') {
                    deque.push(temp);
                } else if (sign == '-') {
                    deque.push(-temp);
                } else if (sign == '*') {
                    deque.push(deque.pop() * temp);
                } else if (sign == '/') {
                    deque.push(deque.pop() / temp);
                }
                sign = s.charAt(i);
                temp = 0;
            }
        }
      //加起来的得数
        while (!deque.isEmpty()) {
            //System.out.println(deque.peek());
            result += deque.pop();
        }
        return result;
    }
}

测试结果:

image.png
image.png

健壮性也很强,可以加负数

image.png
image.png