题解 | #表达式求值#

package main

import "strconv"
/**
 * 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
*/

var m = map[string]int{
	"+": 1,
	"-": 1,
	"*": 2,
	"/": 2,

}

func solve( s string ) int {
	// write code here



	nums := make([]int, 0)
	opts := make([]string, 0)
	i := 0 ;
	nums = append(nums, 0)
	for  i < len(s)  {

		ch := string(s[i])
		if ch == "(" {
			opts = append(opts, ch)
		} else if ch == ")"{
			nums, opts = calc(nums, opts, "")
			if len(opts) > 0 && opts[len(opts) - 1] == "(" {
				opts = opts[0:len(opts) - 1]
			}

		} else if isNumber(ch) {
			j := i+1
			for j < len(s) && isNumber(string(s[j])){
				j++
			}
			t := s[i:j]
			num, _ := strconv.Atoi(t)
			nums = append(nums, num)
			i = j
			continue
		} else {
			if len(opts) == 0 {
				opts = append(opts, ch)
			} else if len(opts)>0 {
				opt := opts[len(opts) - 1]
				if m[ch] > m[opt] {
					opts = append(opts, ch)
				} else {
					nums, opts = calc(nums, opts, ch)
					opts = append(opts, ch)
				}

			}
		}

		i++

	}
	nums, opts = calc(nums, opts, "")
	return nums[len(nums) - 1]
}

func isNumber(ch string) bool {
	if ch >= "0" && ch <= "9" {
		return true
	}
	return false
}


func calc(nums []int, opts []string, outSide string) ([]int,[]string)  {

	for len(opts) > 0 && len(nums) > 1 {
		ch := opts[len(opts) - 1]
		if ch == "(" {
			return nums, opts
		}
		if outSide != "" && m[ch] < m[outSide] {
			return nums, opts
		}
		opts = opts[0:len(opts) - 1]

		num1 := nums[len(nums) - 1]
		num2 := nums[len(nums) - 2]
		nums = nums[0:len(nums) - 2]

		res := 0
		if ch == "+" {
			res = num2 + num1
		} else if ch == "-" {
			res = num2 - num1
		} else if ch == "*" {
			res = num2 * num1
		} else if ch == "/" {
			res = num2 / num1
		}
		nums = append(nums, res)
	}
	return nums, opts

}