Python3

class Solution:
    def myAtoi(self, s: str) -> int:
        sign, idx = 1, 0
        while idx < len(s) and s[idx] == ' ': idx += 1

        if idx < len(s) and s[idx] == '+': idx += 1
        elif idx < len(s) and s[idx] == '-': idx += 1; sign = -1 

        num = 0
        while idx < len(s) and s[idx] >= '0' and s[idx] <= '9':
            num = num * 10 + int(s[idx])
            idx += 1

        num *= sign
        maxv = 1 << 31
        if num > 0 and num > maxv - 1: num = maxv - 1
        if num < 0 and num < -maxv: num = -maxv

        return num

Go

const maxv int64 = 1 << 31

func myAtoi(s string) int {
    // go 中 int，系统多少位就多少位
    var (
        i    int
        sign int = 1
        num  int64 
    )

    for i = 0; i < len(s); i++ {
        if s[i] != ' ' {
            break
        }
    }

    if i < len(s) && s[i] == '-' {
        sign = -1
        i++
        fmt.Println("have - ")
    } else if i < len(s) && s[i] == '+' {
        i++
    }

    for ; i < len(s) && s[i] >= '0' && s[i] <= '9'; i++ {
        num = num * 10 + int64(s[i] - '0')
        if num > maxv {
            num = maxv
        }
    }
    num *= int64(sign)
    if num > maxv - 1 {
        num = maxv - 1
    }
    if num < -maxv {
        num = -maxv
    }

    return int(num)
}