不懂为什么都写平衡树，明明 set 就好了啊，思路跟平衡树差不多，实现起来较为简单。
int n, m, k;
int s[N];
string s1, s2;
int cnt[N];
vector<int> t;
set<int> p[N];
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> s1 >> s2;
n = s1.size(), m = s2.size();
s1 = " " + s1, s2 = " " + s2;
for(int i = 1; i <= n; i ++) {
s[i] = s1[i] - 'a';
cnt[s[i]] ++;
p[s[i]].insert(i);
}
for(int i = 1; i <= m; i ++) {
int x = s2[i] - 'a';
if(cnt[x]) t.push_back(x);
}
if(t.size() != m) {
cout << -1 << '\n';
return 0;
}
int cur = 0, now = -1;
k = 1;
while(cur < t.size()) {
auto it = p[t[cur]].lower_bound(now + 1);
if(it == p[t[cur]].end()) {
now = -1;
k ++;
continue;
}
cur ++;
now = *it;
}
cout << (LL)(k - 1) * n + now << '\n';
return 0;