8. String to Integer

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.

将一个字符串转化为 int 型。

1. null or empty string
2. white spaces
3. +/- sign
4. calculate real value
5. handle min & max

public int atoi(String str) {
if (str == null || str.length() < 1)
return 0;

// trim white spaces
str = str.trim();

char flag = '+';

// check negative or positive
int i = 0;
if (str.charAt(0) == '-') {
flag = '-';
i++;
} else if (str.charAt(0) == '+') {
i++;
}
// use double to store result
double result = 0;

// calculate value
while (str.length() > i && str.charAt(i) >= '0' && str.charAt(i) <= '9') {
result = result * 10 + (str.charAt(i) - '0');
i++;
}

if (flag == '-')
result = -result;

// handle max and min
if (result > Integer.MAX_VALUE)
return Integer.MAX_VALUE;

if (result < Integer.MIN_VALUE)
return Integer.MIN_VALUE;

return (int) result;
}