[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;

}