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=0; 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=0; i<len; i++) {
        if (n[i] != '0') {
            full_zero = false;
            break;
        }
    }
    while (i<len) {
        cout<<n[i++];
    }
    return full_zero;
}

int main() {
    string is;
    int N = 0;
    cin>>N;
    
    vector<string> segs(N);
    for (int i=0; i<N; i++) {
        cin>>segs[i];
    }
    
    int len = segs.size();

    sort(segs.begin(), segs.end(), mycmp);
    
    bool zero = true;
    if (len > 0) {
        for (int i=0; i<len; i++) {
            if (zero) {
                zero = print_no_leading_zero(segs[i]);
            } else {
                cout<<segs[i];
            }
        }
        
    } 
    if (len < 1 || zero) {
        cout<<0;
    }
    cout<<endl;
    return 0;
}

要不是以前做过还是想不到的