National Day Training Day 1(10.1)

B : magic
Score : 90->100
Diff : 1
Comment :
Examing : Easy.
After Examing : ???
Aft. : OHHHHHH:

#include 
using namespace std;

int main() {
    freopen("coin.in", "r", stdin);
    freopen("coin.out", "w", stdout);
    int l;cin >> l;
    string seq;cin >> seq;
    string re_seq;
    char head=seq[0];
    for (int i=1;i<l;i++) {
        if (seq[i]!=head) {
            re_seq += head;
            head = seq[i];
        }
    }
    re_seq += head;
    if (seq[l-1] != head) re_seq += seq[l-1];
    if (re_seq[0] == '1') cout << re_seq.length();
    else cout << re_seq.length() / 2 * 2;
    return 0;
}

if (re_seq[0] == '1') cout << re_seq.length();
else cout << re_seq.length() / 2 * 2;

That should be :

if (re_seq[re_seq.length()-1] == '1') cout << re_seq.length();
else cout << re_seq.length()-1;

Finally: