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::io::{self, BufRead};

pub fn lower_bound<T: Ord>(vec: &[T], val: T) -> usize {
  let mut lo = 0;
  let mut hi = vec.len();
  while hi - lo > 0 {
    let p = (hi + lo) / 2;
    if vec[p] < val {
      lo = p + 1;
    } else {
      hi = p;
    }
  }
  return lo;
}

fn to_index(c: char) -> usize {
  c as usize - 'a' as usize
}

fn main() {
  let stdin = io::stdin();
  let mut lines = stdin.lock().lines();
  let s: Vec<char> = lines.next().unwrap().unwrap().chars().collect();
  let t: Vec<char> = lines.next().unwrap().unwrap().chars().collect();
  let mut cs: Vec<Vec<usize>> = vec![vec![]; 26];
  for i in 0..s.len() {
    let j = to_index(s[i]);
    cs[j].push(i);
  }
  let mut i: usize = 0;
  let mut round: usize = 0;
  for &c in &t {
    let j = to_index(c);
    if cs[j].len() == 0 {
      println!("-1");
      return;
    }
    let mut k = lower_bound(&cs[j], i);
    if k == cs[j].len() {
      k = 0;
      round += 1;
    }
    i = cs[j][k] + 1;
  }
  println!("{}", round * s.len() + i);
}