/**
* Source : https://oj.leetcode.com/problems/string-to-integer-atoi/
*
* Created by lverpeng on 2017/7/4.
*
* Implement atoi to convert a string to an integer.
*
* Hint: Carefully consider all possible input cases. If you want a challenge,
* please do not see below and ask yourself what are the possible input cases.
*
* Notes:
* It is intended for this problem to be specified vaguely (ie, no given input specs).
* You are responsible to gather all the input requirements up front.
*
*
* Requirements for atoi:
*
* The function first discards as many whitespace characters as necessary until the first
* non-whitespace character is found. Then, starting from this character, takes an optional
* initial plus or minus sign followed by as many numerical digits as possible, and interprets
* them as a numerical value.
*
* The string can contain additional characters after those that form the integral number,
* which are ignored and have no effect on the behavior of this function.
*
* If the first sequence of non-whitespace characters in str is not a valid integral number,
* or if no such sequence exists because either str is empty or it contains only whitespace
* characters, no conversion is performed.
*
* If no valid conversion could be performed, a zero value is returned. If the correct value
* is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648)
* is returned.
*
*/
public class IntegerParser {
/**
* 将字符串转化为int
* 考虑各种输入：
* 输入包含非数字
* 超出int范围
* 可能是负数
*
* @param str
* @return
*/
public int parse (String str) throws Exception {
if (str == null || str.length() == 0) {
return 0;
}
int result = 0;
boolean flag = true;
if (str.charAt(0) == '-') {
flag = false;
str = str.substring(1);
} else if (str.charAt(0) == '+') {
flag = true;
str = str.substring(1);
}
for (int i = 0; i < str.length(); i++) {
if (!isdDigit(str.charAt(i))) {
throw new IllegalArgumentException("is not a number");
}
if (result > Integer.MAX_VALUE / 10 || result < Integer.MIN_VALUE / 10) {
throw new Exception("overflow");
}
result = result * 10 + str.charAt(i) - 48;
}
if (!flag) {
result = 0 - result;
}
return result;
}
private boolean isdDigit (char c) {
if (c >= 48 && c <= 57) {
return true;
}
return false;
}
public static void main(String[] args) throws Exception {
IntegerParser parser = new IntegerParser();
System.out.println(parser.parse("123"));
System.out.println(parser.parse("+123"));
System.out.println(parser.parse("-123"));
System.out.println(parser.parse("123ABC"));
}
}