IOI '96 P5 - Longest Prefix

#include <iostream>
#include <string>
#include <vector>
#include <set>

using namespace std;

const int MAX_LEN = 10;

int main() {
    set<string> primitives;
    string s, t;
    while (cin >> t && t != ".") primitives.insert(t);
    while (cin >> t) s += t;
    vector<bool> can(1+s.size());
    can[0] = true;
    int longest;
    for (int i = 0; i <= s.size(); ++i) {
        if (!can[i]) continue;
        longest = i;
        for (int j = 1; j <= MAX_LEN && i+j <= s.size(); ++j) {
            if (primitives.count(s.substr(i, j))) can[i+j] = true;
        }
    }
    cout << longest << endl;
    return 0;
}