P50726: F005A. Paraules de Fibonacci

#include <iostream>
#include <vector>
#include <string>
using namespace std;


string concatenar(string a, string b) {
    int tam_a = a.size();
    int tam_b = b.size();
    string c(tam_a + tam_b, ' ');
    for (int i = 0; i < tam_a; ++i) c[i] = a[i];
    for (int i = 0; i < tam_b; ++i) c[i+tam_a] = b[i];
    return c;
}

int pos(string s, const vector<string>& v) {
    for (int i = 0; i < 16; ++i) {
        if (v[i] == s) return i;
    }
    return -1;
}


int main() {
    vector<string> v(16);
    v[0] = "a";
    v[1] = "b";
    for (int i = 2; i < 16; ++i) v[i] = concatenar(v[i-2], v[i-1]);
    string s;
    while (cin >> s) {
        int aux = pos(s, v);
        if (aux < 0) cout << s << " no es de Fibonacci" << endl;
        else cout << s << " es la paraula numero " << aux + 1 << endl;
    }
}

//JosepRivaille