8. Go implementation of string conversion integer (ATOI) and leetcode

8. String conversion integers (atoi)

Please come to realize a  myAtoi(string s)  function , Enable it to convert a string to a 32 Bit signed integer （ similar C/C++ Medium atoi function ）.

function  myAtoi(string s) The algorithm is as follows ：

Read in strings and discard useless leading spaces
Check the next character （ Suppose you haven't reached the end of the character yet ） Positive or negative , Read the character （ If there is ）. Determine whether the final result is negative or positive . If neither exists , Suppose the result is positive .
Read in the next character , Until you reach the next non numeric character or the end of the input . The rest of the string will be ignored .
Convert the numbers read in the previous steps into integers （ namely ,"123" -> 123, "0032" -> 32）. If you don't read in the numbers , Then the integer is 0 . Change the symbol if necessary （ From step 2 Start ）.
If the number of integers exceeds 32 Bit signed integer range [−231,  231 − 1] , You need to truncate this integer , Keep it in this range . say concretely , Less than −231 The integer of should be fixed to −231 , Greater than 231 − 1 The integer of should be fixed to 231 − 1 .
Returns an integer as the final result .

Be careful ：

The white space character in this question only includes the space character ' ' .
Except for the leading space or the rest of the string after the number , Do not ignore Any other character .
 

Example  1：

Input ：s = "42"
Output ：42
explain ： The bold string is the character that has been read in , The caret is the character currently read .
The first 1 Step ："42"（ No characters are currently read in , Because there are no leading spaces ）
         ^
The first 2 Step ："42"（ No characters are currently read in , Because it doesn't exist here '-' perhaps '+'）
         ^
The first 3 Step ："42"（ Read in "42"）
           ^
Parse to get an integer 42 .
because "42" In scope [-231, 231 - 1] Inside , The final result is 42 .

Example  2：

Input ：s = "   -42"
Output ：-42
explain ：
The first 1 Step ："   -42"（ Read in leading space , But ignore ）
            ^
The first 2 Step ："   -42"（ Read in '-' character , So the result should be negative ）
             ^
The first 3 Step ："   -42"（ Read in "42"）
               ^
Parse to get an integer -42 .
because "-42" In scope [-231, 231 - 1] Inside , The final result is -42 .

Example  3：

Input ：s = "4193 with words"
Output ：4193
explain ：
The first 1 Step ："4193 with words"（ No characters are currently read in , Because there are no leading spaces ）
         ^
The first 2 Step ："4193 with words"（ No characters are currently read in , Because it doesn't exist here '-' perhaps '+'）
         ^
The first 3 Step ："4193 with words"（ Read in "4193"; Because the next character is not a number , So read in stop ）
             ^
Parse to get an integer 4193 .
because "4193" In scope [-231, 231 - 1] Inside , The final result is 4193 .
 

Tips ：

0 <= s.length <= 200
s By the English letters （ Uppercase and lowercase ）、 Numbers （0-9）、' '、'+'、'-' and '.' form

Traverse ： Simulation is enough

func myAtoi(s string) int {
    //  Traverse 
    s = strings.TrimSpace(s)
	result := 0
	flag := 1
	for i, v := range s {
		if v >= '0' && v <= '9' {
			result = result*10 + int(v-'0')
		} else if v == '-' && i == 0 {
			flag = -1
		} else if v == '+' && i == 0 {
			flag = 1
		} else {
			break
		}
		if result > math.MaxInt32 {
			if flag == -1 {
				return math.MinInt32
			}
			return math.MaxInt32
		}
	}
	return flag * result
}