LeetCode 387. First Unique Character in a String

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Description

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.

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Analysis

Solution written in Cpp

class Solution {
public:
    int firstUniqChar(string s) {
        std::array<uint32_t, 26> alpha {0};
        for (auto c: s) {
            alpha[c - 'a']++;
        }

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

        return -1;
    }
};

Solution written in Rust

impl Solution {
    pub fn first_uniq_char(s: String) -> i32 {
        let mut alpha = [0; 26];
        s.chars().for_each(|c| {
            let index = c as usize - 'a' as usize;
            alpha[index] += 1;
        });

        let mut i = 0;
        for c in s.chars() {
            let index = c as usize - 'a' as usize;
            if alpha[index] == 1 {
                return i;
            }
            i += 1;
        }

        -1
    }
}