D. Make a Power of Two, Easy
- We just have to figure out that it is asking for prefix of main string, with power of 2, to be matched.
- The string which matched the most, will be tracked.
Code sample
```cpp
void solve() {
std::string s;
std::cin >> s;
int res = 1E9;
for (int i = 0; i < 64; i++) {
std::string t = std::to_string(1ULL << i);
int k = 0;
for (int j = 0; j < int(s.length()); j++) {
if (k < int(t.length()) && s[j] == t[k]) {
k++;
}
}
res = std::min(res, int(s.length()) + int(t.length()) - 2 * k);
}
std::cout << res << "\n";
}
```