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# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using static Input;

public class Prog
{
    public struct Pair { public int x, y; public Pair(int x, int y) { this.x = x; this.y = y; } }
    public static void Solve()
    {
        string s = NextString();
        string t = NextString();
        if (s == t) { Console.WriteLine(1); return; }
        Dictionary<char, List<int>> d = new Dictionary<char, List<int>>();
        for (char c = 'a'; c <= 'z'; c++) d[c] = new List<int>();
        for (int i = 0; i < s.Length; i++) { d[s[i]].Add(i); }

        int now_ind = -1;
        long ans = 0;
        for (int i = 0; i < t.Length; i++)
        {
            //t[i]があるか探す
            if (d[t[i]].Count() == 0) { ans = -1; break; }
            else
            {
                if (1 <= i && t[i - 1] == t[i] && d[t[i]].Count() == 1)
                {
                    ans++;
                    //Console.WriteLine("=" + now_ind.ToString());
                }
                else if (now_ind < d[t[i]].First())
                {
                    //周期変更なし
                    now_ind = d[t[i]].First();
                    //Console.WriteLine("<" + now_ind.ToString());
                }
                else if (d[t[i]].Last() < now_ind)
                {
                    //必ず周期変更する
                    ans++;
                    now_ind = d[t[i]].First();
                    //Console.WriteLine(">" + now_ind.ToString());
                }
                else
                {
                    //二部探索で超える場所を探す
                    now_ind = UpperBound(d[t[i]], now_ind + 1);
                    //Console.WriteLine("0" + now_ind.ToString());
                }
            }
        }
        if (ans == -1) Console.WriteLine(-1);
        else Console.WriteLine(ans * (long)(s.Length) + now_ind + 1);
    }
    private static int UpperBound(List<int> list, int n)
    {
        int a = 0, b = list.Count();
        while (b - a != 1)
        {
            int x = (a + b) / 2;
            if (list[x] > n) b = x;
            else a = x;
        }
        return b;
    }
    private static int LowerBound(List<int> list, int n)
    {
        int a = 0, b = list.Count();
        if (list[b - 1] <= n) return b - 1;
        else if (list[a] > n) return -1;
        while (b - a != 1)
        {
            int x = (a + b) / 2;
            if (list[x] <= n) a = x;
            else b = x;
        }
        return a;
    }
    public static void Main()
    {
        var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
        Console.SetOut(sw);
        Solve();
        Console.Out.Flush();
    }
}
public class Input
{
    public const long MOD = 1000000007;
    public const int INF = 1000000007;
    private static Queue<string> q = new Queue<string>();
    private static void Confirm() { if (q.Count == 0) foreach (var s in Console.ReadLine().Split(' ')) q.Enqueue(s); }
    public static int NextInt() { Confirm(); return int.Parse(q.Dequeue()); }
    public static long NextLong() { Confirm(); return long.Parse(q.Dequeue()); }
    public static string NextString() { Confirm(); return q.Dequeue(); }
    public static double NextDouble() { Confirm(); return double.Parse(q.Dequeue()); }
    public static int[] LineInt() { return Console.ReadLine().Split(' ').Select(int.Parse).ToArray(); }
    public static long[] LineLong() { return Console.ReadLine().Split(' ').Select(long.Parse).ToArray(); }
    public static string[] LineString() { return Console.ReadLine().Split(' ').ToArray(); }
    public static double[] LineDouble() { return Console.ReadLine().Split(' ').Select(double.Parse).ToArray(); }
}