AtoI.java

public class AtoI {

    static int ConvertAtoI(String s){
        int n = s.length();
        int r = 0;
        int sign =1;
        int index =0;

        //Spaces
        while(index<n && s.charAt(index) == ' '){
            index++;
        }

        //Sign
        if(index<n && s.charAt(index) =='-' ){
            sign = -1;
            index++;
        }

        else{
            if(index<n && s.charAt(index) == '+'){
                sign = 1;
                index++;
            }
        }

        while(index<n && Character.isDigit(s.charAt(index))){
            int digit = s.charAt(index) - '0';
            if(r>=Integer.MAX_VALUE/10 || (r==Integer.MAX_VALUE/10 && digit > Integer.MAX_VALUE %10)){
                return sign == 1 ?Integer.MAX_VALUE : Integer.MIN_VALUE;
            }
            else{
                if(r<= Integer.MIN_VALUE /10 ){
                    return Integer.MIN_VALUE;
                }
            }
            r = r*10+digit;
            index++;
        }

        return r * sign;
    }
    public static void main(String[] args) {
        System.out.println(ConvertAtoI("-9568"));
    }
}