LeetCode/cpp/first-unique-character-in-a-string.cpp

#include <algorithm>
#include <array>
#include <cassert>
#include <string>
#include <utility>

class Solution {
  public:
    int firstUniqChar(const std::string &s) {
        std::array<std::pair<int, int>, 26> counters;
        counters.fill(std::make_pair(0, static_cast<int>(s.size())));

        for (auto i = 0; i < static_cast<int>(s.size()); ++i) {
            auto &[count, index] = counters[s[i] - 'a'];

            ++count;
            index = std::min(index, i);
        }

        int min_index = static_cast<int>(s.size());
        for (const auto &[count, index] : counters) {
            if (count != 1) {
                continue;
            }

            min_index = std::min(min_index, index);
        }

        if (min_index == static_cast<int>(s.size())) {
            return -1;
        }
        return min_index;
    }
};

int main() {
    Solution s;

    assert(s.firstUniqChar("leetcode") == 0);
    assert(s.firstUniqChar("loveleetcode") == 2);
    assert(s.firstUniqChar("aabb") == -1);

    return 0;
}