public class Solution {

     public int myAtoi(String s) {

         if (s == null || s.length() < 1) {

             return 0;

         }

         int i = 0;

         while (i < s.length() && s.charAt(i) == ' ') {

             i++;

         }

         if (i == s.length()) {

             return 0;

         }

         boolean isN = false;

         if (s.charAt(i) == '-') {

             isN = true;

             i++;

         } else if (s.charAt(i) == '+') {

             i++;

         }

         double r = 0;

         for (; i < s.length(); i++) {

             if (s.charAt(i) < '0' || s.charAt(i) > '9') {

                 break;

             }

             r = r * 10 + (s.charAt(i) - '0');

         }

         if (isN) {

             r = -r;

             if (r < Integer.MIN_VALUE) {

                 return Integer.MIN_VALUE;

             }

         } else if (r > Integer.MAX_VALUE) {

             return Integer.MAX_VALUE;

         }

         return (int)r;

     }

 }