#include <algorithm>
#include <cassert>
#include <vector>

class Solution {
public:
    char nextGreatestLetter(const std::vector<char>& letters, char target)
    {
        auto it = std::lower_bound(letters.begin(), letters.end(), target + 1);
        return it == letters.end() ? letters.front() : *it;
    }
};

int main()
{
    Solution s;

    assert((s.nextGreatestLetter(std::vector { 'c', 'f', 'j' }, 'a') == 'c'));
    assert((s.nextGreatestLetter(std::vector { 'c', 'f', 'j' }, 'c') == 'f'));
    assert((s.nextGreatestLetter(std::vector { 'x', 'x', 'y', 'y' }, 'z') == 'x'));

    return 0;
}