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 BITSearch {
    size: usize,
    num_alphabet: usize,
    array: Vec<usize>,
    acc_arrays: HashMap<usize, Vec<i64>>,
}
impl BITSearch {
    fn new(xs: &Vec<usize>, num_alphabet: usize) -> BITSearch {
        let n = xs.len();
        let mut acc_arrays = HashMap::new();
        fn add(arr: &mut Vec<i64>, idx: usize, w: i64) {
            let mut x = idx + 1;
            while x < arr.len() {
                arr[x] += w;
                let xi = x as i64;
                x += (xi&-xi) as usize;
            }
        }
        for a in 0..num_alphabet {
            let mut arr = vec![0; n + 1];
            for idx in 0..n {
                if xs[idx] == a {
                    add(&mut arr, idx, 1);
                }
            }
            acc_arrays.insert(a, arr);
        }
        BITSearch  {
            size: n,
            num_alphabet: num_alphabet,
            array: vec![0; n + 1],
            acc_arrays: acc_arrays,
        }
    }
    fn sum_up(&self, alphabet: usize, idx: usize) -> i64 { // [0, idx)
        let mut sum = 0;
        let mut x = idx;
        while x > 0 {
            sum += self.acc_arrays.get(&alphabet).unwrap()[x];
            let xi = x as i32;
            x -= (xi&-xi) as usize;
        }
        sum
    }
    fn sum(&self, alphabet: usize, range: Range<usize>) -> i64 {
        self.sum_up(alphabet, range.end) - self.sum_up(alphabet, range.start)
    }
    fn search(&self, alphabet: usize, range: Range<usize>) -> Option<usize> {
        if self.sum(alphabet, range.clone()) == 0 {
            return None
        }
        let mut left = range.start;
        let mut right = range.end;
        for _ in 0..30 {
            let mid = (left + right) / 2;
            if self.sum(alphabet, range.start..mid) == 0 {
                left = mid;
            } else {
                right = mid;
            }
        }
        Some(right)
    }
}

fn conv(s: String) -> Vec<usize> {
    let a = 'a' as u8;
    s.chars().map(|c| (c as u8 - a) as usize).collect()
}

fn main() {
    let mut sc = Scanner::new();
    let s = conv(sc.cin());
    let t = conv(sc.cin());

    {
        use std::collections::HashMap;
        let mut a = vec![0; 26];
        let mut b = vec![0; 26];
        for &i in s.iter() { a[i] += 1; }
        for &i in t.iter() { b[i] += 1; }
        let mut ok = true;
        for i in 0..26 {
            if a[i] == 0 && b[i] > 0 {
                ok = false;
                break
            }
        }
        if !ok {
            put!(-1);
            return
        }
    }
    {
        let bit = BITSearch::new(&s, 26);
        let mut ans = 0;
        let mut ansmod = 0;
        for &c in t.iter() {
            if let Some(i) = bit.search(c, ansmod..s.len()) {
                ans += i - ansmod;
                ansmod = i;
            } else {
                if let Some(i) = bit.search(c, 0..s.len()) {
                    ans += s.len() - ansmod + i;
                    ansmod = i;
                }
            }
        }
        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()
    }
}