题解 | 小牛的作业

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

int main() {
    string s, t;
    cin >> s >> t;

    if (s.length() < t.length()) {
        cout << -1 << endl;
        return 0;
    }

    // 统计频率
    vector<int> cnt_s(26, 0), cnt_t(26, 0);

    // 只取 s 的前 t.length() 个字符
    for (int i = 0; i < s.length(); ++i)
        cnt_s[s[i] - 'a']++;

    for (char c : t)
        cnt_t[c - 'a']++;

    int changes = 0;
    for (int i = 0; i < 26; ++i) {
        if (cnt_s[i] < cnt_t[i])
            changes += cnt_t[i] - cnt_s[i];
    }
    changes+=s.size()-t.size();

    cout << changes << endl;
    return 0;
}