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::collections::HashMap;
fn solve() {
    let s = std::io::stdin();
    let mut sc = Scanner { stdin: s.lock() };
    let s = sc.chars();
    let t = sc.chars();
    let mut s_to_vec = HashMap::new();
    for i in 0..s.len() {
        s_to_vec.entry(s[i]).or_insert(Vec::new()).push(i);
    }
    let mut idx = 0;
    let mut result = 0;
    let mut diff = 0;
    for x in t.iter() {
        // println!("{} {}", idx, result);
        if let Some(v) = s_to_vec.get(&x) {
            if let Some(res) = v.lower_bound(&idx) {
                idx = v[res] + 1;
                diff = idx - 1;
            } else {
                result += 1;
                idx = v[v.lower_bound(&0).unwrap()] + 1;
                diff = idx - 1;
            }
        } else {
            println!("-1");
            return;
        }
    }
    println!("{}", s.len() * result + diff + 1);
}

fn main() {
    std::thread::Builder::new()
        .stack_size(64 * 1024 * 1024) // 64MB
        .spawn(|| solve())
        .unwrap()
        .join()
        .unwrap();
}
use std::cmp::Ordering;

pub trait BinarySearch<T> {
    fn lower_bound(&self, x: &T) -> Option<usize>;
    fn upper_bound(&self, x: &T) -> Option<usize>;
}

impl<T: Ord> BinarySearch<T> for [T] {
    //greater than or equal
    fn lower_bound(&self, x: &T) -> Option<usize> {
        let mut left = 0;
        let mut right = self.len();
        let mut result = None;
        while left < right {
            let med = (left + right) / 2;
            match self[med].cmp(x) {
                Ordering::Less => {
                    left = med + 1;
                }
                Ordering::Equal | Ordering::Greater => {
                    result = Some(med);
                    right = med;
                }
            }
        }
        result
    }
    fn upper_bound(&self, x: &T) -> Option<usize> {
        let mut left = 0;
        let mut right = self.len();
        let mut result = None;
        while left < right {
            let med = (left + right) / 2;
            match self[med].cmp(x) {
                Ordering::Equal | Ordering::Less => {
                    left = med + 1;
                }
                Ordering::Greater => {
                    result = Some(med);
                    right = med;
                }
            }
        }
        result
    }
}

//snippet from kenkoooo
pub struct Scanner<R> {
    stdin: R,
}

impl<R: std::io::Read> Scanner<R> {
    pub fn read<T: std::str::FromStr>(&mut self) -> T {
        use std::io::Read;
        let buf = self
            .stdin
            .by_ref()
            .bytes()
            .map(|b| b.unwrap())
            .skip_while(|&b| b == b' ' || b == b'\n' || b == b'\r')
            .take_while(|&b| b != b' ' && b != b'\n' && b != b'\r')
            .collect::<Vec<_>>();
        unsafe { std::str::from_utf8_unchecked(&buf) }
            .parse()
            .ok()
            .expect("Parse error.")
    }
    pub fn read_line(&mut self) -> String {
        use std::io::Read;
        let buf = self
            .stdin
            .by_ref()
            .bytes()
            .map(|b| b.unwrap())
            .skip_while(|&b| b == b'\n' || b == b'\r')
            .take_while(|&b| b != b'\n' && b != b'\r')
            .collect::<Vec<_>>();
        unsafe { std::str::from_utf8_unchecked(&buf) }
            .parse()
            .ok()
            .expect("Parse error.")
    }
    pub fn vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read()).collect()
    }

    pub fn chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
}