LeetCode 467. Unique Substrings in Wraparound String

class Solution {
public:
    int findSubstringInWraproundString(string p) {
        int f[26] = {0}, cnt = 0;
        for (int i = 0; i < p.size(); ++i) {
            cnt = i && (p[i] - p[i - 1] + 26) % 26 == 1 ? cnt + 1 : 1;
            f[p[i] - 'a'] = max(f[p[i] - 'a'], cnt);
        }
        return accumulate(f, f + 26, 0);
    }
};