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 (1.42.0) (judge verdict: Accepted)

use std::io::Read;
use std::collections::HashMap;

fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();

    let answer = solve(&buf);

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

fn solve(input: &str) -> String {
    let mut iterator = input.split_whitespace();

    let s: Vec<char> = iterator.next().unwrap().chars().collect();
    let t: Vec<char> = iterator.next().unwrap().chars().collect();

    let mut map: HashMap<char, Vec<usize>> = HashMap::new();
    for i in 0..s.len() {
        map.entry(s[i]).or_insert(Vec::new()).push(i);
    }

    let mut prev: isize = -1;
    let mut offset: usize = 0;
    for i in 0..t.len() {
        if let Some(v) = map.get(&t[i]) {
            let mut ok: isize = v.len() as isize;
            let mut ng: isize = -1;
            while (ok - ng).abs() > 1 {
                let mid = (ok + ng) / 2;
                if (v[mid as usize] + offset) as isize > prev {
                    ok = mid;
                } else {
                    ng = mid;
                }
            }
            if ok == v.len() as isize {
                offset += s.len();
                prev = (v[0] + offset) as isize;
            } else {
                prev = (v[ok as usize] + offset) as isize;
            }
        } else {
            return "-1".to_string();
        }
    }
    (prev + 1).to_string()
}