209. First Unique Character in a String

Description

Find the first unique character in a given string. You can assume that there is at least one unique character in the string.

Example

For "abaccdeff", return 'b'.

解题：返回仅出现一次，并且排在最前面的那个元素，而不是返回第一个不同的元素，一开始理解错了。如果仅仅对于ASCII中的256个字符，可以用数组来保存每个元素出现的次数。而对于Unicode中的元素，最好用HashMap来做。代码如下：

 public class Solution {
     /**
      * @param str: str: the given string
      * @return: char: the first unique character in a given string
      */
     public char firstUniqChar(String str) {
         // Write your code here
         HashMap<Character, Integer>map = new HashMap<Character, Integer>();
         for(int i = 0; i < str.length(); i++){
             char temp = str.charAt(i);
             if(map.containsKey(temp)){
                 map.put(temp, map.get(temp) + 1);
             }else{
                 map.put(temp, 1);
             }
         }
         for(int i = 0; i < str.length(); i++)
             if(map.get(str.charAt(i)) == 1)
                  return str.charAt(i);

         return str.charAt(0);

     }
 }