第一个只出现一次的字符

s = "abaccdeff"
返回 ‘b‘

s = "" 
返回 ‘ ‘

 1 class Solution {
 2     public char firstUniqChar(String s) {
 3         char[] array = s.toCharArray();
 4         Map<Character,Boolean> map = new HashMap<>();
 5         for(char c : array){
 6             map.put(c,!map.containsKey(c));
 7         }
 8         for(char ch : array){
 9             if(map.get(ch)){
10                 return ch;
11             }
12         }
13         return ‘ ‘;
14     }
15 }