LeetCode 1055. Shortest Way to Form String

Problem Statement

use std::collections::HashMap;


use std::collections::HashSet;

impl Solution {
    pub fn shortest_way(source: String, target: String) -> i32 {
        let (ss, st, mut ans) = (source.len(), target.len(), 1);
        let mut set = HashSet::new();
        for c in source.chars() {
            set.insert(c);
        }
        let (mut i, mut j) = (0, 0);
        while i < st {
            if !set.contains(&target.chars().nth(i).unwrap()) {
                return -1;
            }
            while j < ss && source.chars().nth(j).unwrap()
                != target.chars().nth(i).unwrap() {
                j += 1;
            }
            if j == ss {
                j = 0; i -= 1; ans += 1;
            } else {
                j += 1;
            }
            i += 1;
        }

        return ans;
    }
}