LeetCode 0389 - Find the Difference

Input:
s = "abcd"
t = "abcde"

Output:
e

Explanation:
'e' is the letter that was added.

class Solution {
public:
    char findTheDifference(const std::string& s, const std::string& t) {
        std::vector<int> sCount = std::vector<int>(26, 0);
        std::vector<int> tCount = std::vector<int>(26, 0);

        for(const auto& c : s) {
            sCount[c - 'a']++;
        }
        for(const auto &c : t) {
            tCount[c - 'a']++;
        }

        int index = 0;
        for(int i = 0; i < sCount.size(); i++) {
            if(tCount[i] == sCount[i] + 1) {
                index = i;
                break;
            }
        }

        return index + 'a';
    }
};