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)

fn read_stdin() -> String {
    use std::io::Read;
    let mut input = String::new();
    std::io::stdin().read_to_string(&mut input).unwrap();
    input
}

fn scan<'a, I: Iterator<Item = &'a str>, T: std::str::FromStr>(tokens: &mut I) -> T {
    tokens.next().unwrap().parse().ok().unwrap()
}

fn main() {
    let input = read_stdin();
    let tokens = &mut input.split_whitespace();
    let s: String = scan(tokens);
    let t: String = scan(tokens);
    let mut pos = vec![Vec::new(); 26];
    for (i, b) in s.bytes().enumerate() {
        pos[b as usize - b'a' as usize].push(i + 1);
    }
    let mut cur = 0;
    let mut wrap = 0;
    for b in t.bytes() {
        let p = &pos[b as usize - b'a' as usize];
        if p.is_empty() {
            println!("-1");
            return;
        }
        if let Some(tmp) = min_more_than(cur, p) {
            cur = tmp;
        } else {
            wrap += 1;
            cur = p[0];
        }
    }
    println!("{}", wrap * s.len() + cur);
}

fn min_more_than(x: usize, v: &[usize]) -> Option<usize> {
    if v.is_empty() {
        return None;
    }
    if v[0] > x {
        return Some(v[0]);
    }
    let mut a: usize = 0;
    let mut b: usize = v.len();
    while a + 1 < b {
        let c = (a + b) / 2;
        if v[c] <= x {
            a = c;
        } else {
            b = c;
        }
    }
    if b == v.len() {
        None
    } else {
        Some(v[b])
    }
}