PAT 1038. Recover the Smallest Number

#include <iostream>
#include <cstdlib>
#include <vector>
#include <algorithm>

using namespace std;

bool mycmp(const string& a, const string& b) {
    string ta = a + b;
    string tb = b + a;

    int len = ta.length();

    for (int i=; i<len; i++) {
        if (ta[i] > tb[i]) {
            return false;
        } else if (ta[i] < tb[i]){
            return true;
        }
    }
    return true;
}

bool print_no_leading_zero(string &n) {
    int len = n.length();
    bool full_zero = true;
    int i;
    for (i=; i<len; i++) {
        if (n[i] != '') {
            full_zero = false;
            break;
        }
    }
    while (i<len) {
        cout<<n[i++];
    }
    return full_zero;
}

int main() {
    string is;
    int N = ;
    cin>>N;

    vector<string> segs(N);
    for (int i=; i<N; i++) {
        cin>>segs[i];
    }

    int len = segs.size();

    sort(segs.begin(), segs.end(), mycmp);

    bool zero = true;
    if (len > ) {
        for (int i=; i<len; i++) {
            if (zero) {
                zero = print_no_leading_zero(segs[i]);
            } else {
                cout<<segs[i];
            }
        }

    }
    if (len <  || zero) {
        cout<<;
    }
    cout<<endl;
    return ;
}

要不是以前做过还是想不到的