Solution2.cpp

class Solution {
public:
    int rotatedDigits(int n) {
        string s = to_string(n);
        int m = s.size();
        int f[m][2];
        memset(f, -1, sizeof(f));
        auto dfs = [&](this auto&& dfs, int i, int ok, bool limit) -> int {
            if (i >= m) {
                return ok;
            }
            if (!limit && f[i][ok] != -1) {
                return f[i][ok];
            }
            int up = limit ? s[i] - '0' : 9;
            int ans = 0;
            for (int j = 0; j <= up; ++j) {
                if (j == 0 || j == 1 || j == 8) {
                    ans += dfs(i + 1, ok, limit && j == up);
                } else if (j == 2 || j == 5 || j == 6 || j == 9) {
                    ans += dfs(i + 1, 1, limit && j == up);
                }
            }
            if (!limit) {
                f[i][ok] = ans;
            }
            return ans;
        };
        return dfs(0, 0, true);
    }
};