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)

#![allow(unused_imports, unused_macros, dead_code)]

macro_rules! min {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        if let Some(z) = it.next() {
            Some(it.fold(z, |x, y| min!(x, y)))
        } else {
            None
        }
    }};
    ($x:expr) => ($x);
    ($x:expr, $($ys:expr),*) => {{
        let t = min!($($ys),*);
        if $x < t { $x } else { t }
    }}
}
macro_rules! max {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        if let Some(z) = it.next() {
            Some(it.fold(z, |x, y| max!(x, y)))
        } else {
            None
        }
    }};
    ($x:expr) => ($x);
    ($x:expr, $($ys:expr),*) => {{
        let t = max!($($ys),*);
        if $x > t { $x } else { t }
    }}
}


macro_rules! ewriteln {
    ($($args:expr),*) => { let _ = writeln!(&mut std::io::stderr(), $($args),*); };
}
macro_rules! trace {
    ($x:expr) => { ewriteln!(">>> {} = {:?}", stringify!($x), $x) };
    ($($xs:expr),*) => { trace!(($($xs),*)) }
}
macro_rules! put {
    (.. $x:expr) => {{
        let mut it = $x.iter();
        if let Some(x) = it.next() { print!("{}", x); }
        for x in it { print!(" {}", x); }
        println!("");
    }};
    ($x:expr) => { println!("{}", $x) };
    ($x:expr, $($xs:expr),*) => { print!("{} ", $x); put!($($xs),*) }
}

const M: i64 = 1_000_000_007;

use std::ops::Range;
use std::collections::HashMap;
struct SeqSearch<T> {
    raw: Vec<T>,
    acc: HashMap<T, Vec<usize>>,
}
impl<T> SeqSearch<T>
where T: std::hash::Hash + Eq + Copy
{
    fn new(xs: &Vec<T>) -> SeqSearch<T> {
        SeqSearch { raw: xs.to_vec(), acc: HashMap::new() }
    }
    fn len(&self) -> usize { self.raw.len() }
    fn new_alphabet(&mut self, alphabet: T) {
        if self.acc.contains_key(&alphabet) {
            return
        }
        let n = self.raw.len();
        let mut ac = vec![0; n + 1];  // ac = count alphabet xs[0, i)
        for i in 0..n {
            ac[i + 1] = ac[i] + if self.raw[i] == alphabet { 1 } else { 0 };
        }
        self.acc.insert(alphabet, ac);
    }
    fn count(&mut self, alphabet: T, range: Range<usize>) -> usize {
        self.new_alphabet(alphabet);
        let ac = self.acc.get(&alphabet).unwrap();
        ac[range.end] - ac[range.start]
    }
    fn search(&mut self, alphabet: T, range: Range<usize>) -> Option<usize> {
        if self.count(alphabet, range.clone()) == 0 {
            return None
        }
        let mut left = range.start;
        let mut right = range.end;
        for _ in 0..100 {
            let mid = (left + right) / 2;
            if self.count(alphabet, range.start..mid) == 0 {
                left = mid;
            } else {
                right = mid;
            }
        }
        Some(left)
    }
}

fn main() {
    let mut sc = Scanner::new();
    let s: Vec<char> = sc.cin::<String>().chars().collect();
    let t: Vec<char> = sc.cin::<String>().chars().collect();
    let mut ss = SeqSearch::new(&s);
    let mut ans = 0;
    let mut last = 0;
    for &c in t.iter() {
        if let Some(i) = ss.search(c, last..s.len()) {
            ans += i - last + 1;
            last = i + 1;
        } else if let Some(i) = ss.search(c, 0..s.len()) {
            ans += s.len() - last + i + 1;
            last = i + 1;
        } else {
            put!(-1);
            return
        }
    }
    put!(ans);
}

use std::io::{self, Write};
use std::str::FromStr;
use std::collections::VecDeque;

struct Scanner { stdin: io::Stdin, buffer: VecDeque<String>, }
impl Scanner {
    fn new() -> Self { Scanner { stdin: io::stdin(), buffer: VecDeque::new() } }
    fn cin<T: FromStr>(&mut self) -> T {
        while self.buffer.len() == 0 {
            let mut line = String::new();
            let _ = self.stdin.read_line(&mut line);
            for w in line.split_whitespace() {
                self.buffer.push_back(String::from(w));
            }
        }
        self.buffer.pop_front().unwrap().parse::<T>().ok().unwrap()
    }
}