class Solution {
    public int shortestWay(String source, String target) {
        int n = source.length();
        int m = target.length();
        boolean validLetter[] = new boolean[26];
        // record exist letter in s
        for(int i = 0; i< n; i++){
            validLetter[source.charAt(i) - 'a'] = true;
        }
        // i and j are indexes of source and target
        int i = 0;
        int j = 0;
        int count = 0;
        while(j < m){
            //
            if(!validLetter[target.charAt(j) - 'a']){
                return -1;
            }
            if(source.charAt(i) == target.charAt(j)){
                j++;
            }
            i++;
            if(i == n){
                i = 0;
                count++;
            }
        }
        if(i != 0) count++;
        return count;
    }
}