Leetcode 387. First Unique Character in a String

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.

Code (Java):

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class Solution {     public int firstUniqChar(String s) {         if (s == null || s.length() == 0) {             return -1;         }           int[] counts = new int[26];           for (int i = 0; i < s.length(); i++) {             char c = s.charAt(i);             counts[c - 'a']++;         }           for (int i = 0; i < s.length(); i++) {             char c = s.charAt(i);             if (counts[c - 'a'] == 1) {                 return i;             }         }           return -1;     } }