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8. String to Integer (atoi) 👎

  • Time: $O(n)$
  • Space: $O(1)$
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class Solution {
 public:
  int myAtoi(string s) {
    trim(s);
    if (s.empty())
      return 0;

    const int sign = s[0] == '-' ? -1 : 1;
    if (s[0] == '+' || s[0] == '-')
      s = s.substr(1);

    long num = 0;

    for (const char c : s) {
      if (!isdigit(c))
        break;
      num = num * 10 + (c - '0');
      if (sign * num < INT_MIN)
        return INT_MIN;
      if (sign * num > INT_MAX)
        return INT_MAX;
    }

    return sign * num;
  }

 private:
  void trim(string& s) {
    s.erase(0, s.find_first_not_of(' '));
    s.erase(s.find_last_not_of(' ') + 1);
  }
};
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class Solution {
  public int myAtoi(String s) {
    s = s.strip();
    if (s.isEmpty())
      return 0;

    final int sign = s.charAt(0) == '-' ? -1 : 1;
    if (s.charAt(0) == '+' || s.charAt(0) == '-')
      s = s.substring(1);

    long num = 0;

    for (final char c : s.toCharArray()) {
      if (!Character.isDigit(c))
        break;
      num = num * 10 + (c - '0');
      if (sign * num <= Integer.MIN_VALUE)
        return Integer.MIN_VALUE;
      if (sign * num >= Integer.MAX_VALUE)
        return Integer.MAX_VALUE;
    }

    return sign * (int) num;
  }
}
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class Solution:
  def myAtoi(self, s: str) -> int:
    s = s.strip()
    if not s:
      return 0

    sign = -1 if s[0] == '-' else 1
    if s[0] in {'-', '+'}:
      s = s[1:]

    num = 0

    for c in s:
      if not c.isdigit():
        break
      num = num * 10 + ord(c) - ord('0')
      if sign * num <= -2**31:
        return -2**31
      if sign * num >= 2**31 - 1:
        return 2**31 - 1

    return sign * num
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