输入只有2行, 分别为字符串S和T (1 <= |S|, |T| <= 100,000), 输入保证字符串S和T只由小写字母构成。

输出最小的k, 满足T ∈Subsequence(S ^ k), 若不存在这样的k, 则输出-1

#pragma GCC diagnostic error "-std=c++11"

#include <bits/stdc++.h>

#define _ ios_base::sync_with_stdio(0);cin.tie(0);

#include <typeinfo>

using namespace std;

const int N =   + ;

char s[N], t[N];

void Init(int * a, int n){ for(int i = ; i < n; i++) a[i] = ;}

int Work(){

    int lens = strlen(s), lent = strlen(t);

    set<int> next[];

    int vis[]; Init(vis, );

    for(int i =  ; i < lens; i++)

        vis[s[i] - 'a'] = , next[s[i]-'a'].insert(i);

    for(int i = ; i < lent; i++) if(!vis[t[i]-'a']) return -;

    int cur = , k = ;

    set<int>::iterator it;

    for(int i = ; i < lent; i++){

        int p = t[i] - 'a';

        if((it = next[p].lower_bound(cur)) != next[p].end()) cur = (*it) + ;

        else cur = , k++, i--;

    }

    return k;

}

int main(){ _

    while(cin >> s >> t){

        cout << Work() << endl;

    }

}