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.

public boolean isNumber(String s) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(s==null||s.length()==0){
            return false;
        }
        //continuous zeros from beginning since begin is true
        int cont = 0;
        boolean hasDot = false;
        boolean begin = false;
        boolean end = false;
        boolean hasSign = false;
        boolean hasE = false;
        
        for(int i=0;i<s.length();i++){
            char c = s.charAt(i);
            
            
            if(c=='+'||c=='-'){
                if(hasSign||begin){
                    return false;
                }else{
                    hasSign = true;
                }
                continue;
            }
            
            if(c=='e'){
                if(hasE||!begin){
                    return false;
                }else{
                    return isInteger(s.substring(i+1));
                    //return true;
                }
            }
            
            if(c=='.'){
                if(hasDot||end){
                    return false;
                }else{
                    hasDot = true;
                }
                continue;
            }
            
            if(c==' '){
                if((begin ||hasSign) && !end){
                    end=true;
                }
                continue;
            }
            
            if(!(isDigit(s,i))){
                return false;
            }else{
                if(end){
                    return false;
                }else{
                    if(!begin){
                        begin=true;
                    }
                }
            }
            
            
        }
        
        if(!begin){
            return false;
        }
        return true;
        
        
    }
    public boolean isInteger(String s){
        if(s==null||s.length()==0){
            return false;
        }
        if(s.length()==1 && isDigit(s,0)){
            return true;
        }
        char c = s.charAt(0);
        if(c=='0'){
            return ifAllSpace(s.substring(1));
        }
        int zeors = 0;
        for(int i=0;i<s.length();i++){
            if(i==0){
                if(c=='+'||c=='-'){
                    return isIntegerWithoutSign(s.substring(i+1));
                }else
                if(!isDigit(s,i)){
                    return false;
                }
            }else
            if(!isDigit(s,i)){
                if(c==' '){
                    return ifAllSpace(s.substring(i+1));
                }else{
                    return false;
                }
            }
        }
        return true;
    }
    
    public boolean ifAllSpace(String s){
        for(int i=0;i<s.length();i++){
            if(s.charAt(i)!=' '){
                return false;
            }
        }
        return true;
    }
    
    public boolean isIntegerWithoutSign(String s){
        if(s==null||s.length()==0){
            return false;
        }
        if(s.length()==1 && isDigit(s,0)){
            return true;
        }
        char c = s.charAt(0);
        if(c=='0'){
            return false;
        }
        for(int i=0;i<s.length();i++){
            if(!isDigit(s,i)){
                if(c==' '){
                    return ifAllSpace(s.substring(i));
                }else{
                    return false;
                }
            }
        }
        return true;
    }
    
    public boolean isDigit(String s,int index){
        char c = s.charAt(index);
        if(c<(int)'0' || c>(int)'9'){
            return false;
        }
        return true;
    }

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