[LeetCode 008] String to Integer (atoi)

String to Integer (atoi)

Implementation

public class Solution {
    public int myAtoi(String str) {
        if (str == null || str.length() == 0) {
            return 0;
        }
        int sign = 1;
        int index = 0;
        /* remove the leading white spaces */
        // check index isn't out of bound
        while (index < str.length() && str.charAt(index) == ' ') {
            index++;
        }
        /* set sign of number */
        if (index < str.length() && (str.charAt(index) == '+' ||str.charAt(index) == '-')) {
            sign = str.charAt(index) == '+'? 1: -1;
            index++;
        }


        int result = 0;
        final int THRESHOLD = Integer.MAX_VALUE / 10; /*  */
        while (index < str.length() && str.charAt(index) >= '0' && str.charAt(index) <='9' ) {
            /*
                check of result will be overflow
                1. the last digit of MAX is 7.
                2. the last digit of MIN is 8.
            */
            if (result > THRESHOLD || (result == THRESHOLD && str.charAt(index) > '7')) {
                return sign == 1? Integer.MAX_VALUE: Integer.MIN_VALUE;
            }
            else {
                result = result * 10 + str.charAt(index) - '0';
                index++;
            }
        }
        return result * sign;
    }
}