Problem:
Score : 500 points

Problem Statement

Given are two strings s and t consisting of lowercase English letters. Determine if there exists an integer i satisfying the following condition, and find the minimum such i if it exists.

Let s' be the concatenation of 10^{100} copies of s. t is a subsequence of the string {s'}_1{s'}_2\ldots{s'}_i (the first i characters in s').

Notes

A subsequence of a string a is a string obtained by deleting zero or more characters from a and concatenating the remaining characters without changing the relative order. For example, the subsequences of contest include net, c, and contest.

Constraints

1 \leq |s| \leq 10^5

1 \leq |t| \leq 10^5

s and t consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

s
t

Output

If there exists an integer i satisfying the following condition, print the minimum such i; otherwise, print -1.

Sample Input 1

contest
son

Sample Output 1

10

t = son is a subsequence of the string contestcon (the first 10 characters in s' = contestcontestcontest...), so i = 10 satisfies the condition.

On the other hand, t is not a subsequence of the string contestco (the first 9 characters in s'), so i = 9 does not satisfy the condition.

Similarly, any integer less than 9 does not satisfy the condition, either. Thus, the minimum integer i satisfying the condition is 10.

Sample Input 2

contest
programming

Sample Output 2

-1

t = programming is not a substring of s' = contestcontestcontest.... Thus, there is no integer i satisfying the condition.

Sample Input 3

contest
sentence

Sample Output 3

33

Note that the answer may not fit into a 32-bit integer type, though we cannot put such a case here.

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main()
{
    string s, t;
    cin >> s >> t;

    vector<vector<ll>> alpha(26);
    for(ll i = 0; i < s.size(); i++)
    {
        alpha[ s[i] - 'a'].push_back(i);
    }

    ll ans = 0;
    ll count = 0;
    ll tpos = 0;
    ll npos = 0;
    while(tpos < t.size())
    {
        ll al = t[tpos] - 'a';
        if(alpha[al].empty())
        {
            cout << -1 << endl;
            return 0;
        }
        auto itr = lower_bound(alpha[al].begin(), alpha[al].end(), npos);
        if(itr == alpha[al].end())
        {
            npos = 0;
            count++;
            continue;
        }
        npos = *itr;
        tpos++;
    }
    ans = count * s.size() + npos + 1;
    cout << ans << endl;
}