Leetcode•Apr 23, 2025
First Unique Character in a String
Hazrat Ali
Leetcode
Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.
Example 1:
Input: s = "leetcode"
Output: 0
Explanation:
The character 'l' at index 0 is the first character that does not occur at any other index.
Example 2:
Input: s = "loveleetcode"
Output: 2
Example 3:
Input: s = "aabb"
Output: -1
Constraints:
1 <= s.length <= 105sconsists of only lowercase English letters.
Solution
/**
* @param {string} s
* @return {number}
*/
const firstUniqChar = s => {
const map = {};
for (let c of s) {
map[c] = ~~map[c] + 1;
}
for (let i = 0; i < s.length; i++) {
if (map[s[i]] === 1) {
return i;
}
}
return -1;
};