1+ /*
2+ Author: Andy, nkuwjg@gmail.com
3+ Date: Jan 25, 2015
4+ Problem: Valid Number
5+ Difficulty: Hard
6+ Source: https://oj.leetcode.com/problems/valid-number/
7+ Notes:
8+ Validate if a given string is numeric.
9+ Some examples:
10+ "0" => true
11+ " 0.1 " => true
12+ "abc" => false
13+ "1 a" => false
14+ "2e10" => true
15+ Note: It is intended for the problem statement to be ambiguous. You should gather all
16+ requirements up front before implementing one.
17+
18+ Solution: This finite-state machine solution. Learn from fuwutu & snakeDling.
19+ */
20+
21+ public class Solution {
22+ public boolean isNumber (String s ) {
23+ int start =0 ,end =s .length () -1 ;
24+ boolean dot =false ,exp =false ,digit =false ;
25+ while (start <=end && (s .charAt (start ) ==' ' )) ++start ;
26+ while (start <=end && (s .charAt (end ) ==' ' )) --end ;
27+ if (start <=end && (s .charAt (start ) =='+' ||s .charAt (start ) =='-' )) ++start ;
28+ if (start >end )return false ;
29+ for ( ;start <=end ; ++start ) {
30+ if (Character .isDigit (s .charAt (start )))digit =true ;
31+ else if (s .charAt (start ) =='e' ||s .charAt (start ) =='E' ) {
32+ if (exp ==true ||digit ==false ||start ==end )return false ;
33+ exp =true ;
34+ }else if (s .charAt (start ) =='.' ) {
35+ if (dot ==true ||exp ==true )return false ;
36+ if (digit ==false &&start ==end )return false ;
37+ dot =true ;
38+ }else if (s .charAt (start ) =='+' ||s .charAt (start ) =='-' ) {
39+ if (start ==end )return false ;
40+ if (s .charAt (start -1 ) !='e' &&s .charAt (start -1 ) !='E' )return false ;
41+ }else return false ;
42+ }
43+ return true ;
44+ }
45+ }
