栈:用golang实现简单计算器

题目简介：给你一个字符串表达式 s ，请你实现一个基本计算器来计算并返回它的值。注意:不允许使用任何将字符串作为数学表达式计算的内置函数，比如 eval()

示例 1：

输入：s = "1 + 1"
输出：2

示例 2：

输入：s = " 2-1 + 2 "
输出：3

示例 3：

输入：s = "(1+(4+5+2)-3)+(6+8)"
输出：23

实现的思路还是用栈的思路，以下是完整的golang实现代码

package main

import (
    "fmt"
    "testing"
)

func calculate(s string) int {
    stack := []int{}
    num := 0
    sign := 1
    result := 0

    for i := 0; i < len(s); i++ {
       char := s[i]

       if char >= '0' && char <= '9' {
          num = num*10 + int(char-'0')
       } else if char == '+' {
          result += sign * num
          num = 0
          sign = 1
       } else if char == '-' {
          result += sign * num
          num = 0
          sign = -1
       } else if char == '(' {
          // Push the result and sign onto the stack, for later
          stack = append(stack, result)
          stack = append(stack, sign)
          // Reset result and sign for the new sub-expression
          result = 0
          sign = 1
       } else if char == ')' {
          // Evaluate the expression to the left with result,
          num = 0
          // Multiply the result by the sign before the parenthesis
          result *= stack[len(stack)-1]
          stack = stack[:len(stack)-1]
          // Add to the next operand on the top.
          result += stack[len(stack)-1]
          stack = stack[:len(stack)-1]
       }
    }
    // If there are no more characters to parse, but there's a number left, then it should be added to the result
    result += sign * num
    return result
}

func TestCalculate(t *testing.T) {
    s1 := "1 + 1"
    s2 := " 2-1 + 2 "
    s3 := "(1+(4+5+2)-3)+(6+8)"

    fmt.Println(calculate(s1)) // 输出: 2
    fmt.Println(calculate(s2)) // 输出: 3
    fmt.Println(calculate(s3)) // 输出: 23
}