[LeetCode] NO. 387 First Unique Character in a String

Posted 2020-08-06

[题目]

Given a string, find the first non-repeating character in it and return it‘s index. If it doesn‘t exist, return -1.

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

Note: You may assume the string contain only lowercase letters.

[题目解析] 根据题意，思路比较简单，遍历字符串，用map存储对应字符以及出现次数，再次遍历原字符串，当出现第一个出现一次的字符时，返回对应的index即可，考虑到Note中提示的字符串只考虑小写字母组成的情况，可以用一个26位的数组表示map结构，代码如下。

   public int firstUniqChar(String s) {
        if(null == s || 0 == s.length() ) return -1;
    	int[] hash = new int[26];
    	char[] array = s.toCharArray();
        for(int i = 0; i < array.length; i++){     	
        	int num = array[i] - ‘a‘;
        	hash[num]++;
        }
        for(int i = 0; i < array.length; i++){
        	int num = array[i] - ‘a‘;
        	if(hash[num] == 1){
        		return i;
        	}
        }
        return -1;
   }