String to Integer

Implement atoi to convert a string to an integer.

Hint:

Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes:

It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

Solution:

  1. public class Solution {
  2.   public int myAtoi(String str) {
  3.     if (str == null) {
  4.       return 0;
  5.     }
  7.     // trim the leading and trailing spaces
  8.     str = str.trim();
  10.     if (str.length() == 0) {
  11.       return 0;
  12.     }
  14.     char[] chars = str.toCharArray();
  16.     boolean positive = true;
  18.     int i = 0;
  20.     if (chars[0] == '-') {
  21.       positive = false;
  22.       i = 1;
  23.     }
  25.     if (chars[0] == '+') {
  26.       i = 1;
  27.     }
  29.     int num = 0;
  31.     while (i < chars.length) {
  32.       char ch = chars[i++];
  34.       if (ch < '0' || ch > '9') {
  35.         return num;
  36.       }
  38.       int d = (int)(ch - '0');
  40.       if (positive) {
  41.         if (num > (Integer.MAX_VALUE - d) / 10) {
  42.           return Integer.MAX_VALUE;
  43.         }
  44.         num = num * 10 + d;
  45.       } else {
  46.         if (num < (Integer.MIN_VALUE + d) / 10) {
  47.           return Integer.MIN_VALUE;
  48.         }
  49.         num = num * 10 - d;
  50.       }
  51.     }
  53.     return num;
  54.   }
  55. }