Have a look it this solution. As we are dealing with integers, they only hold 32-bit. 2^31 < x <= -2^31. So here we use a try catch as the 32bit integer can raise NumberFormat Exception which will be caught by the catch block.

class Solution {
    public int myAtoi(String str) {

        int flag=0, sign = 0;
        int n = str.length();
        StringBuilder st = new StringBuilder();
        int i =0;

        //clear white spaces
        while(i<n && str.charAt(i) == ' '){
            ++i;
        }

        //overflow of string
        if (i>=n){
            return 0;
        }

        //checking sign and not allowing more than one sign, will return 0 if there is ++,+-,--
        while(i<n && (str.charAt(i) == '+' || str.charAt(i) == '-')){
            if (sign >= 1){
                return 0;
            }
            else{
           st.append((str.charAt(i++) == '+') ? '+': '-');
            sign++;
            }

        }

        //checking if character is digit
        while(i<n && Character.isDigit(str.charAt(i))){
            st.append(str.charAt(i++));
            flag = 1;
        }

        //return 0 if no digits
        if(flag == 0)
            return 0;

        //to check if the number is within the int range
        try{
            return Integer.parseInt(st.toString());

        }
        catch(NumberFormatException e){
            return (st.charAt(0) == '-') ? Integer.MIN_VALUE : Integer.MAX_VALUE;
        }



    }
}