8 - String to Integer (atoi)

 JAVA

• class Solution {
      public int myAtoi(String s) {
          if (s == null) return 0;
          int n = s.length();
          if (n == 0) return 0;
          int i = 0;
          while (s.charAt(i) == ' ') {
              if (++i == n) return 0;
          }
          int sign = 1;
          if (s.charAt(i) == '-') sign = -1;
          if (s.charAt(i) == '-' || s.charAt(i) == '+') ++i;
          int res = 0, flag = Integer.MAX_VALUE / 10;
          for (int j = i; j < n; ++j) {
              if (s.charAt(j) < '0' || s.charAt(j) > '9') break;
              if (res > flag || (res == flag && s.charAt(j) > '7'))
                  return sign > 0 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
              res = res * 10 + (s.charAt(j) - '0');
          }
          return sign * res;
      }
  }

C#

public partial class Solution
{
    public int MyAtoi(string str)
    {
        int i = 0;
        long result = 0;
        bool minus = false;
        while (i < str.Length && char.IsWhiteSpace(str[i]))
        {
            ++i;
        }
        if (i < str.Length)
        {
            if (str[i] == '+')
            {
                ++i;
            }
            else if (str[i] == '-')
            {
                minus = true;
                ++i;
            }
        }
        while (i < str.Length && char.IsDigit(str[i]))
        {
            result = result * 10 + str[i] - '0';
            if (result > int.MaxValue)
            {
                break;
            }
            ++i;
        }
        if (minus) result = -result;
        if (result > int.MaxValue)
        {
            result = int.MaxValue;
        }
        if (result < int.MinValue)
        {
            result = int.MinValue;
        }
        return (int)result;
    }
}