BowWow and the Timetable
Hazrat Ali
In the city of Saint Petersburg, a day lasts for 21 minutes. From the main station of Saint Petersburg, a train departs after 1 minute, 4 minutes, 16 minutes, and so on; in other words, the train departs at time 4k for each integer k≥0. Team BowWow has arrived at the station at the time s and it is trying to count how many trains have they missed; in other words, the number of trains that have departed strictly before time s. For example if s=20, then they missed trains which have departed at 1, 4 and 16. As you are the only one who knows the time, help them!
Note that the number s will be given you in a binary representation without leading zeroes.
The first line contains a single binary number s (0≤s<21) without leading zeroes.
Output a single number — the number of trains which have departed strictly before the time s.
100000000
4
101
2
10100
3
Solution
#include <bits/stdc++.h>
using namespace std;
int main()
{
string s;
cin >> s;
bool pot = s.find('1', 1) == string::npos;
int ans = pot ? s.size() / 2 : (s.size() + 1) / 2;
cout << ans << endl;
return 0;
}