题解 | #表达式求值#

/**
 * 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
*/
func solve( s string ) int {
    i := 0
    var helper func(string) int 
    helper = func (s string) int {
        sign := byte('+')
        num := 0
        bytes := []byte(s)
        stack := []int{}
        for i < len(bytes) {
            b := s[i]
            i++
            if isDigit(b) {
                num = num * 10 + int(b-'0')
            }
            if b == '(' {
                num = helper(s)
            }
            if !isDigit(b) && b != ' ' || i == len(bytes) {
                switch sign {
                case '+' : 
                    stack = append(stack, num)
                case '-' :
                    stack = append(stack, -num)
                case '*' :
                    stack[len(stack)-1] *= num
                case '/' :
                    stack[len(stack)-1] /= num
                }
                sign = b
                num = 0
            }
            if b == ')' {
                break
            }    
        }
        return sum(stack)
    }
    return helper(s)
}
func isDigit(b byte) bool {
    return b >= '0' && b <= '9'
}
func sum(stack []int) int {
    s := 0
    for _, num := range stack {
        s += num
    }
    return s
}