8. String to Integer (atoi)

https://leetcode.com/problems/string-to-integer-atoi/

C++

class Solution {
public:
    int myAtoi(string s) {
        if (s.empty()) {
            return 0;
        }

        int i = 0;
        int result = 0;
        int sign = 1;

        while (i < s.length() && s[i] == ' ') {
            i++;
        }
        if (i >= s.length()) {
            return 0;
        }

        if (s[i] == '+') {
            i++;
        } else if (s[i] == '-') {
            sign = -1;
            i++;
        }

        while (i < s.length() && s[i] >= '0' && s[i] <= '9') {
            result = result * 10 + (s[i] - '0');
            i++;
        }

        return sign * result;
    }
};

Go

import "math"

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

  var result int32 = 0
  var sign int32 = 1
  i := 0

  for str[i] == ' ' {
    i++
  }

  if str[i] == '+' {
    i++
  } else if str[i] == '-' {
    sign = -1
    i++
  }

  for i < len(str) && str[i] >= '0' && str[i] <= '9' {
    num := int32(str[i] - '0')

    if result > (math.MaxInt32-num)/10 {
      if sign > 0 {
        return math.MaxInt32
      }
      return math.MinInt32
    }

    result = result*10 + num
    i++
  }

  return int(sign * result)
}

JavaScript

/**
 * @param {string} str
 * @return {number}
 */
var myAtoi = function(str) {
  const INT_MAX = 2147483647
  const INT_MIN = -2147483648

  if (!str) {
    return 0
  }

  var i = 0
  var result = 0
  var sign = 1

  str = str.trim()

  if (str[i] === '+') {
    i++
  } else if (str[i] === '-') {
    sign = -1
    i++
  }

  while (i < str.length && str[i] >= '0' && str[i] <= '9') {
    let num = +str[i]

    if (result > (INT_MAX - num) / 10) {
      return sign > 0 ? INT_MAX : INT_MIN
    }

    result = result * 10 + num
    i++
  }

  return sign * result
}

Python

class Solution(object):

    def myAtoi(self, s):
        """
        :type s: str
        :rtype: int
        """
        INT_MAX, INT_MIN = 2147483647, -2147483648
        if not s:
            return 0
        i, result, sign = 0, 0, 1
        s = s.strip()

        if s[i] == '+':
            i += 1
        elif s[i] == '-':
            sign = -1
            i += 1

        while i < len(s) and s[i] >= '0' and s[i] <= '9':
            num = int(s[i])
            if result > (INT_MAX - num) / 10:
                return INT_MAX if sign > 0 else INT_MIN
            result = result * 10 + num
            i += 1

        return sign * result