First Unique Character In A String Problem


Description

LeetCode Problem 387.

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:

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Input: s = "leetcode"
Output: 0

Example 2:

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Input: s = "loveleetcode"
Output: 2

Example 3:

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Input: s = "aabb"
Output: -1

Constraints:

  • 1 <= s.length <= 10^5
  • s consists of only lowercase English letters.


Sample C++ Code

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class Solution {
public:
    int firstUniqChar(string s) {
        int ht[26] = {0};
        
        for (int i = 0; i < s.size(); i ++) {
            ht[s[i] - 'a'] ++;
        }
        
        for (int i = 0; i < s.size(); i ++) {
            if (ht[s[i] - 'a'] == 1)
                return i;
        }
        
        return -1;
    }
};




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