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func myAtoi(str string) int {
	if len(str) == 0 {
		return 0
	}

	result := 0
	u := -1 //有无符号
	e := -1 //错误位第几位
	for n, v := range str {
		if v < 48 || v > 57 {
			if v == 43 || v == 45 { //+-号
				if result != 0 {
					e = n
					break
				}
				if u >= 0 {
					return 0
				}
				u = n
				continue
			}
			if v == 32 { //空格
				if result != 0 {
					e = n
					break
				}
				if u >= 0 { //这里默认符号之后只能跟数字
					return 0
				}
				continue
			}
			e = n
			break
		}
		result += int(v-48) * int(math.Pow(10, float64(len(str)-n-1)))
	}
	if e >= 0 {
		result /= int(math.Pow(10, float64(len(str)-e)))
	}
	if u >= 0 {
		if str[u] == 45 {
			result = -result
		}
	}
	if result > math.MaxInt32 {
		if u >= 0 {
			if str[u] == 45 {
				return math.MinInt32
			}
		}
		result = math.MaxInt32
	}
	if result < math.MinInt32 {
		if u < 0 {
			return math.MaxInt32
		} else {
			if str[u] != 45 {
				return math.MaxInt32
			}
		}
		result = math.MinInt32
	}

	return result
}

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func myAtoi2(str string) int {
	//empty string
	if len(str) == 0 {
		return 0
	}

	index, sign, result := 0, 1, 0
	//remove space
	for i := 0; i < len(str); i++ {
		if str[i] == ' ' {
			index++
		} else {
			break
		}
	}

	//handle sign
	if str[index] == '+' || str[index] == '-' {
		if str[index] == '-' {
			sign = -1
		}
		index++
	}

	//Convert number and avoid overflow
	for i := index; i < len(str); i++ {
		digit := int(str[i] - '0')
		if digit < 0 || digit > 9 {
			break
		}

		if sign == 1 {
			if math.MaxInt32/10 == result || math.MaxInt32/10 < result && math.MaxInt32%10 < digit {
				return math.MaxInt32
			}
		} else {
			if (math.MaxInt32/10 == result || math.MaxInt32/10 < result) && digit > 8 {
				return math.MinInt32
			}
		}

		result = result*10 + digit
		index++
	}

	return result * sign
}