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 Rust (1.15.1) (judge verdict: Accepted)

#![allow(non_snake_case)]
#![allow(unused_variables)]
#![allow(dead_code)]

fn main() {
    let s: Vec<char> = {
        let mut line: String = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
        line.trim().chars().collect()
    };
    let t: Vec<char> = {
        let mut line: String = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
        line.trim().chars().collect()
    };

    // 各アルファベットについて、sの出現位置をメモしておく
    // メモした出現位置用いた二分探索により、次のインデックスを計算する　
    let N = s.len();
    let mut x: std::collections::HashMap<_, _> = (0..26).map(|i| {
        let ascii_code = ('a' as u8) + i;
        (ascii_code as char, vec![])
    }).collect();
    for (i, &c) in s.iter().enumerate() { x.get_mut(&c).unwrap().push(i as i64); }
    for (i, &c) in s.iter().enumerate() { x.get_mut(&c).unwrap().push((i + N) as i64); }
    fn bis<P>(ok: i64, ng: i64, p: P) -> i64
        where P: Fn(i64) -> bool {
        let mid = (ok + ng) / 2;
        if (ok - ng).abs() == 1 {
            ok
        } else if p(mid) {
            bis(mid, ng, p)
        } else {
            bis(ok, mid, p)
        }
    }
    let k: i64 = t.iter().fold(-1, |res, &c| {
        if res == -2 || x[&c].is_empty() { -2 }
        else {
            let i = res % (N as i64);
            let j = bis(x[&c].len() as i64, -1, |j| x[&c][j as usize] > i);
            res + (x[&c][j as usize] - i)
        }
    });
    let ans = if k >= 0 { k + 1 } else { -1 };

    println!("{}", ans);
}