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)

use std::io::*;
use std::str::FromStr;

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

fn main() {
    let A = 26;
    let a = 'a' as usize;

    let s: Vec<usize> = read::<String>().chars().map(|c| c as usize).collect();
    let t: Vec<usize> = read::<String>().chars().map(|c| c as usize).collect();
    let sn = s.len();

    let mut nxt = vec![vec![!0; A]; sn];
    let mut tbl = vec![!0; A];

    for i in (0..sn).rev() {
        tbl[s[i] - a] = sn + i;
    }
    for i in (0..sn).rev() {
        for c in 0..A {
            nxt[i][c] = tbl[c];
        }
        tbl[s[i] - a] = i;
    }

    let mut i = 0;
    for (k, c) in t.iter().enumerate() {
        let t;
        if k == 0 {
            t = tbl[c - a];
        } else {
            t = nxt[i % sn][(c - a) as usize];
        }
        if t == !0 {
            println!("-1");
            return;
        }
        i += (t - (i % sn));
    }
    println!("{}", i + 1);
}