936. Stamping The Sequence

Hard

---

You are given two strings stamp and target. Initially, there is a string s of length target.length with all s[i] == '?'.

In one turn, you can place stamp over s and replace every letter in the s with the corresponding letter from stamp.

• For example, if stamp = "abc" and target = "abcba", then s is "?????" initially. In one turn you can:

  <ul>
  	<li>place <code>stamp</code> at index <code>0</code> of <code>s</code> to obtain <code>"abc??"</code>,</li>
  	<li>place <code>stamp</code> at index <code>1</code> of <code>s</code> to obtain <code>"?abc?"</code>, or</li>
  	<li>place <code>stamp</code> at index <code>2</code> of <code>s</code> to obtain <code>"??abc"</code>.</li>
  </ul>
  Note that <code>stamp</code> must be fully contained in the boundaries of <code>s</code> in order to stamp (i.e., you cannot place <code>stamp</code> at index <code>3</code> of <code>s</code>).</li>

We want to convert s to target using at most 10 * target.length turns.

Return an array of the index of the left-most letter being stamped at each turn. If we cannot obtain target from s within 10 * target.length turns, return an empty array.

Example 1:

Input: stamp = "abc", target = "ababc"
Output:
 [0,2]
Explanation:
 Initially s = "?????".
- Place stamp at index 0 to get "abc??".
- Place stamp at index 2 to get "ababc".
[1,0,2] would also be accepted as an answer, as well as some other answers.

Example 2:

Input: stamp = "abca", target = "aabcaca"
Output:
 [3,0,1]
Explanation:
 Initially s = "???????".
- Place stamp at index 3 to get "???abca".
- Place stamp at index 0 to get "abcabca".
- Place stamp at index 1 to get "aabcaca".

Constraints:

• 1 <= stamp.length <= target.length <= 1000

• stamp and target consist of lowercase English letters.

class Solution:
#.
    def movesToStamp(self, stamp, target):
        def okay(s):
            ret = False
            for c1, c2 in zip(s, stamp):
                if c1 == "?": continue
                elif c1 != c2: return False
                else: ret = True
            return ret
        root, move, mx, arr = "?" * len(target), 0, 10 * len(target), []
        while move < mx:
            pre = move
            for i in range(len(target) - len(stamp) + 1):
                if okay(target[i:i + len(stamp)]):
                    move += 1
                    arr = [i] + arr
                    target = target[:i] + "?" * len(stamp) + target[i + len(stamp):]
            if target == root: return arr
            if move == pre: break
        return []