题目：

题解：

func calculate(s string) (ans int) {ops := []int{1}sign := 1n := len(s)for i := 0; i < n; {switch s[i] {case ' ':i++case '+':sign = ops[len(ops)-1]i++case '-':sign = -ops[len(ops)-1]i++case '(':ops = append(ops, sign)i++case ')':ops = ops[:len(ops)-1]i++default:num := 0for ; i < n && '0' <= s[i] && s[i] <= '9'; i++ {num = num*10 + int(s[i]-'0')}ans += sign * num}}return
}