//standard solution from leetcode.

private static final int maxDiv10 = Integer.MAX_VALUE / 10;

public int atoi(String str) {

int i = 0, n = str.length();

while (i < n && Character.isWhitespace(str.charAt(i))) i++;

int sign = 1;

if (i < n && str.charAt(i) == '+' ) {

i++;

} else if (i < n && str.charAt(i) == ' - ' ) {

sign = - 1;

i++;

}

int num = 0;

while (i < n && Character.isDigit(str.charAt(i))) {

int digit = Character.getNumericValue(str.charAt(i));

if (num > maxDiv10 || num == maxDiv10 && digit >= 8) {

return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;

}

num = num * 10 + digit;

i++;

}

return sign * num;

}