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(non_snake_case, unused)]
use std::cmp::*;
use std::collections::*;
use std::f64::consts::*;

macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $($r)*}
    };
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}

macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };

    ($next:expr, mut $var:ident : $t:tt $($r:tt)*) => {
        let mut $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}

macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, [ $t:tt ]) => {
        {
            let len = read_value!($next, usize);
            (0..len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
        }
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, bytes) => {
        read_value!($next, String).into_bytes()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}
pub trait BinarySearch<T> {
    fn lower_bound(&self, value: &T) -> usize;
    fn upper_bound(&self, value: &T) -> usize;
}

impl<T: Ord> BinarySearch<T> for [T] {
    fn lower_bound(&self, value: &T) -> usize {
        let mut l = 0;
        let mut r = self.len();

        while l != r {
            let m = (l + r) / 2;
            match self[m].cmp(value) {
                Ordering::Less => {
                    l = m + 1;
                }
                Ordering::Equal | Ordering::Greater => {
                    r = m;
                }
            }
        }
        r
    }

    fn upper_bound(&self, value: &T) -> usize {
        let mut l = 0;
        let mut r = self.len();

        while l != r {
            let m = (l + r) / 2;
            match self[m].cmp(value) {
                Ordering::Equal | Ordering::Less => {
                    l = m + 1;
                }
                Ordering::Greater => {
                    r = m;
                }
            }
        }
        l
    }
}

fn main() {
    input! {
        s: chars,
        t: chars,
    }
    let mut cur = 0;
    let mut cnt = 0u64;

    let mut v = vec![vec![]; 28];
    let mut s_ = s.len() as u64;
    let mut t_ = t.len();
    for i in 0..s_ {
        v[(s[i as usize] as u8 - 'a' as u8) as usize].push(i + 1);
    }
    let mut acc = 0u64;
    for i in 0..t_ {
        let acc_char = (t[i] as u8 - 'a' as u8) as usize;
        let v_len = v[acc_char].len();
        if v_len == 0 {
            return println!("-1");
        }
        let idx = v[acc_char].upper_bound(&acc);
        if v_len == idx {
            cnt += 1;
            acc = v[acc_char][0];
        } else {
            acc = v[acc_char][idx];
        }
    }
    let mut ans: u64 = cnt * s_ + acc;
    println!("{}", ans);
}