Shortest Way to Form String Python Solution

lcpy gen -n 1055   # by problem number
lcpy gen -s shortest_way_to_form_string   # by problem name

Input: source = "abc", target = "abcbc"
Output: 2
Explanation: The target "abcbc" can be formed by "abc" and "bc", which are subsequences of source "abc".

Input: source = "abc", target = "acdbc"
Output: -1
Explanation: The target string cannot be constructed from the subsequences of source string due to the character "d" in target string.

Input: source = "xyz", target = "xzyxz"
Output: 3
Explanation: The target string can be constructed as follows "xz" + "y" + "xz".

class Solution:
    # Time: O(m * n)
    # Space: O(1)
    def shortest_way(self, source: str, target: str) -> int:
        m, n = len(source), len(target)
        ans = j = 0
        while j < n:
            i, k = 0, j
            while i < m and k < n:
                if source[i] == target[k]:
                    k += 1
                i += 1
            if k == j:
                return -1
            j = k
            ans += 1
        return ans