387

387. First Unique Character in a String (Easy)

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

Example 2:

Input: s = "loveleetcode"
Output: 2

Example 3:

Input: s = "aabb"
Output: -1

 

Constraints:

• 1 <= s.length <= 105
• s consists of only lowercase English letters.

Companies:
Facebook, Bloomberg, Amazon, Apple, Zillow, Goldman Sachs, Microsoft, Google, Yahoo

Related Topics:
Hash Table, String, Queue, Counting

Similar Questions:

• Sort Characters By Frequency (Medium)
• First Letter to Appear Twice (Easy)

Solution 1.

// OJ: https://leetcode.com/problems/first-unique-character-in-a-string/
// Author: github.com/lzl124631x
// Time: O(S)
// Space: O(1)
class Solution {
public:
    int firstUniqChar(string s) {
        int cnt[26] = {0};
        for (char c : s) cnt[c - 'a']++;
        for (int i = 0; i < s.size(); ++i) {
            if (cnt[s[i] - 'a'] == 1) return i;
        }
        return -1;
    }
};