[LeetCode] Valid Number

Problem:

Validate if a given string is numeric.

Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

Solution1:O(n)

public class Solution {
    public boolean isNumber(String s) {
     if (s==null ){
            return false;
        } 
        s=s.trim();
        if(s.length()==0){
            return false;
        } 
        boolean hasNum=false;
        boolean canSign=true;
        boolean canDot=true;
        boolean canE=false;
        boolean hasE=false;
        int i=0;
        while(i<s.length()){
            char c=s.charAt(i++);
            if (c==' '){
              return false;
            }
            if (c=='+' ||c=='-'){
               if (!canSign){
                   return false;
               }
               canSign=false;
               continue;
            }
           
            if (c=='.'){
               if (!canDot){
                   return false;
               }
               canDot=false;
               canSign=false;
               continue;
            }
           
            if (c=='e'){
               if (!canE||hasE){
                   return false;
               }
               canE=false;
               hasE=true;
               hasNum=false;
               canDot=false;
               canSign=true;
               continue;
            }
            if (c>='0' && c<='9'){
               hasNum=true;
               if (!canE&&!hasE){
                   canE=true;
               }
               canSign=false;
            }
            else{
                return false;
            }
       }
       return hasNum;
    }
}

Solution2:O(n)

public class Solution {
        public boolean isNumber(String s) {  
        if(s.trim().isEmpty()){  
            return false;  
        }  
        String regex = "[-+]?(\\d+\\.?|\\.\\d+)\\d*(e[-+]?\\d+)?";  
        return s.trim().matches(regex); 
    }
}