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/**
 * 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.
 * Requirements for atoi:
 * The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. 
 * Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value.
 * The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.
 * If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed.
 * If no valid conversion could be performed, a zero value is returned. If the correct value is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned.
 */
 
public class Solution {
	public int myAtoi(String str) {
        int index = 0, sign = 1, total = 0;
        //1. Empty string
        if(str.length() == 0) return 0;
    
        //2. Remove Spaces
        while(str.charAt(index) == ' ' && index < str.length())
            index ++;
    
        //3. Handle signs
        if(str.charAt(index) == '+' || str.charAt(index) == '-'){
            sign = str.charAt(index) == '+' ? 1 : -1;
            index ++;
        }
        
        //4. Convert number and avoid overflow
        while(index < str.length()){
            int digit = str.charAt(index) - '0';
            if(digit < 0 || digit > 9) break;
    
            //check if total will be overflow after 10 times and add digit
            if(Integer.MAX_VALUE / 10 < total || Integer.MAX_VALUE / 10 == total && Integer.MAX_VALUE % 10 < digit)
                return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
    
            total = 10 * total + digit;
            index ++;
        }
        return total * sign;
    }


    public int myAtoi(String str) {
        int p = 0, ret = 0;
        while(p < str.length() && Character.isWhitespace(str.charAt(p))) ++p;
        if(p == str.length()) return 0;
        boolean negFlag = (str.charAt(p) == '-');
        if(str.charAt(p) == '+' || str.charAt(p) == '-') ++p;
        for(; p<str.length(); ++p) {
            if(str.charAt(p) > '9' || str.charAt(p) < '0') {
                break;
            }else {
                int digit = str.charAt(p) - '0';
                if(!negFlag && ret > (Integer.MAX_VALUE - digit) / 10) return Integer.MAX_VALUE;
                else if(negFlag && ret < (Integer.MIN_VALUE + digit) / 10) return Integer.MIN_VALUE;
                ret = ret * 10 + (negFlag ? -digit : digit);
            }
        }
        return ret;
        
    } 
}