[LeetCode] 8. String to Integer (atoi)

Implement atoi to convert a string to an integer.

 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;
     }
 }