8. String to Integer (atoi)

class Solution {
    public int myAtoi(String s) {
        int sign =1;
        int index=0;
        
        //ignore lead whitesapce
        while(index<s.length() && s.charAt(index)==' '){
            index++;
        }
        
        // check sign
        if(index<s.length() && s.charAt(index)=='+'){
            index++;
        }else if (index<s.length() && s.charAt(index) == '-'){
            index++;
            sign = -1;
        }
        
        int result = 0;
        // move pointer until it reaches the firt non-digit char
        while(index<s.length() && s.charAt(index)>='0' && s.charAt(index)<='9'){
            int digit = s.charAt(index)-'0';
            
            // Key: if reuslt is just equal to MIN_VALUE will be return from here, 
            // if result is just equal to MAX_VALUE, will be return outside the while loop
            if (Integer.MAX_VALUE/10<result || 
                (Integer.MAX_VALUE/10==result && Integer.MAX_VALUE%10<digit)){
                return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
            }

            result=result*10+digit;
            index++;
        }
        
        return sign*result;
    }
}