java-solutions/src/main/java/leetcode/StringToInteger.java at master · nikoo28/java-solutions · GitHub

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package leetcode;

/**
 * Created by nikoo28 on 7/19/19 2:39 AM
 */

class StringToInteger {

  public int myAtoi(String str) {

    str = str.trim();
    if (str == null || str.length() == 0)
      return 0;

    char firstChar = str.charAt(0);
    int sign = 1, start = 0, len = str.length();
    long sum = 0;

    if (firstChar == '+') {
      sign = 1;
      start++;
    } else if (firstChar == '-') {
      sign = -1;
      start++;
    }

    for (int i = start; i < len; i++) {
      if (!Character.isDigit(str.charAt(i)))
        return (int) sum * sign;
      sum = sum * 10 + str.charAt(i) - '0';

      if (sign == 1 && sum > Integer.MAX_VALUE)
        return Integer.MAX_VALUE;
      if (sign == -1 && (-1) * sum < Integer.MIN_VALUE)
        return Integer.MIN_VALUE;
    }

    return (int) sum * sign;
  }

}