387. First Unique Character in a String

• Difficulty: Easy

• Topics: Hash Table, String

• Similar Questions:

  • Sort Characters By Frequency

Problem:

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.

Solutions:

class Solution {
public:
    int firstUniqChar(string s) {
        int count[26] = {0};
        for (int i = 0; i < s.length(); ++i) {
            ++count[s[i] - 'a'];
        }

        for (int i = 0; i < s.length(); ++i) {
            if (count[s[i] - 'a'] == 1) return i;
        }

        return -1;
    }
};