First Character Appearing Once

Problem

No. 13 - First Character Appearing Only Once
Implement a function to find the first character in a string which only appears once.
For example: It returns ‘b’ when the input is “abaccdeff”.

Solution Least Time

 Character getFirstUnique(char[] w)
 {
  HashMap m = new LinkedHashMap();
  for(int i=0; i< w.length; i++)
  {
   Integer cnt = m.get(w[i]);
   if(cnt == null) m.put(w[i], 1);
   else m.put(w[i], cnt+1);
  }
  
  for(int i=0; i< w.length; i++)
  {
   if(m.get(w[i]) == 1) return w[i];
  }

  return null;
 }

Solution Least Space

 public Character solnNoMem(char[] w)
 {
  for(int i=0; i< w.length; i++)
  {
   int cnt = 0;
   for(int j=0; j< w.length; j++)
   {
    if(i!=j && w[i] == w[j]) {
     cnt =1; break;
    }
   }
   if(cnt==0) return w[i];
  }
  return null;
 }