[算法]String to Integer（atoi）

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.

Analysis

The following cases should be considered for this problem:

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

Java Solution

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;
 
}