209. First Unique Character in a String

Posted 2020-11-19 phdeblog

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：

 1 public class Solution {
 2     /**
 3      * @param str: str: the given string
 4      * @return: char: the first unique character in a given string
 5      */
 6     public char firstUniqChar(String str) {
 7         // Write your code here
 8         HashMap<Character, Integer>map = new HashMap<Character, Integer>();
 9         for(int i = 0; i < str.length(); i++){
10             char temp = str.charAt(i);
11             if(map.containsKey(temp)){
12                 map.put(temp, map.get(temp) + 1);
13             }else{
14                 map.put(temp, 1);
15             }
16         }
17         for(int i = 0; i < str.length(); i++)
18             if(map.get(str.charAt(i)) == 1)
19                  return str.charAt(i);
20         
21         return str.charAt(0);
22                  
23     }
24 }