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::str::FromStr;
use std::fmt::Debug;
use std::cmp;

#[allow(dead_code)]
fn read_as_vec<T>() -> Vec<T>
where T: FromStr, <T as FromStr>::Err : Debug{
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().split_whitespace().map(|c| T::from_str(c).unwrap()).collect()

}

#[allow(dead_code)]
fn read_as_string() -> String{
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    s.trim().to_string()
}

fn append_2nd_positions(appear_pos_vec: &mut Vec<Vec<usize>>, s_len: usize){
    for i in 0..26{
        let original_vec_len = appear_pos_vec[i].len();
        for j in 0..original_vec_len{
            let value_of_2nd_through = appear_pos_vec[i][j]+s_len;
            appear_pos_vec[i].push(
                value_of_2nd_through
            );
        }
    }
}

fn lower_bound(v: &[usize], val: usize) -> usize{
    let mut left = 0;
    let mut right = v.len()-1;

    loop{
        let mid = (left + right)/2;

        if v[mid] < val{
            left = mid+1;
        }else{ // val <= v[mid]
            right = mid;
        }

        //if right - left <= 1{
        if left == right{
            return v[left];
        }
    }
}

fn main(){
    let s = read_as_string();
    let s_len = s.len();
    let t = read_as_string();

    let mut appear_pos_vec: Vec<Vec<usize>> = vec![Vec::new();26];

    for (i, ch) in s.bytes().enumerate(){
        appear_pos_vec[(ch -97) as usize].push(i);
    }

    append_2nd_positions(&mut appear_pos_vec, s.len());

    let mut lower_val: usize = 0;
    let mut num_loop: usize = 0;
    for ch in t.bytes(){
        let ch = (ch - 97) as usize;
        if appear_pos_vec[ch].len() == 0{
            println!("-1");
            return;
        }
        let found_pos = lower_bound(&appear_pos_vec[ch], lower_val);
        //println!("found at {}", found_pos);
        lower_val = found_pos+1;
        if s_len <= lower_val{
            num_loop += 1;
            lower_val -= s_len;
        }
    }
    
    println!("{}", num_loop*s_len+lower_val);
}