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)

#[allow(unused_imports)]
use itertools::Itertools;
#[allow(unused_imports)]
use num::*;
use proconio::input;
#[allow(unused_imports)]
use proconio::marker::*;
#[allow(unused_imports)]
use std::collections::*;

pub fn bsearch<F>(ok: i64, ng: i64, pred: F) -> Option<i64>
where
    F: Fn(i64) -> bool,
{
    let orig_ok = ok;
    let mut ok = ok;
    let mut ng = ng;
    while (ok - ng).abs() > 1 {
        let mid = (ok + ng) / 2;
        if pred(mid) {
            ok = mid;
        } else {
            ng = mid;
        }
    }
    if ok == orig_ok {
        None
    } else {
        Some(ok)
    }
}

fn main() {
    input! {
        s: Chars,
        t: Chars
    };

    let s_len = s.len();
    let mut pos_table = HashMap::new();
    for (i, ch) in s.into_iter().enumerate() {
        pos_table.entry(ch).or_insert(Vec::new()).push(i as i64);
    }
    let mut res = 0;
    let mut cur_pos = -1;
    for ch in t {
        let posv = match pos_table.get(&ch) {
            Some(v) => v,
            _ => {
                println!("-1");
                return;
            }
        };
        let i = bsearch(posv.len() as i64, -1, |x| {
            let p = posv[x as usize];
            cur_pos < p
        });
        if let Some(i) = i {
            let p = posv[i as usize];
            res += p - cur_pos;
            cur_pos = p;
            continue;
        }
        res += s_len as i64 - 1 - cur_pos;
        cur_pos = -1;
        let i = bsearch(posv.len() as i64, -1, |x| {
            let p = posv[x as usize];
            cur_pos < p
        });
        if let Some(i) = i {
            let p = posv[i as usize];
            res += p - cur_pos;
            cur_pos = p;
        } else {
            unreachable!();
        }
    }
    println!("{}", res);
}